With all things being equal the booster simply assists the brake pedal effort required.
This means, in your scenario anyway, the perceived brake pedal effort will be less with the boosted system as compared to the manual system.

If things are set up correctly both will provide proper braking and both can be made to have the same pedal effort. The manual system will likely have a bit more pedal travel than the other due to the smaller bore diameter.
One thing to keep in mind when comparing boosted brakes to manual brakes is the master cylinder bore diameter.
They are often not the same between a boosted and manual system.

Because they are not the same in terms of physics and math, making literal direct comparisons is not an even race.

In real simple terms a smaller master cylinder bore diameter will increase the applied pressure when using the same pedal effort.
A couple things to keep in mind when going to a smaller master cylinder bore.
1) less fluid moved.
2) longer pedal travel required to move the same amount of fluid.

Another factor in pedal effort and fluid volume being moved is the pedal fulcrum point, or leverage.
You can radically alter how the pedal feels to push, as well as the amount of fluid being moved with the location of the pedal fulcrum. A distance change of 1" to the fulcrum location is an exponential change in pedal effort and fluid moved.

I am curious what you are building that may require 6 piston brake calipers?

Thanks for the replies so far. I appreciat all of them.
I too have towed into WI (Rock Falls Raceway) but things change every once in a while and I just wanted to check.

I looked a the WI DOT regs trying ti find any specifics that may apply to me...None do.
I will be under 8000lbs meaning no need to stop at any weight stations.
I have no signage of any kind so I look like just a guy with a truck and trailer.
I drive at 65 max with the trailer, for a number of reasons, so I will be under the posted limit most of the time.
I don't think I will have any issues, but I just wanted to check.
Thanks again everyone.

If I do have troubles, the "emergency escape pod" in the trailer will be fun to get help with.

When I first decided to try the Lock-Right I was careful about figuring out which unit to purchase. The original differential in my truck was a 10.25", 3.55:1 gear, open differential. I got the right parts for that differential. With all the troubles, and subsequent talk with the engineer, we both verified I did have the right stuff...It just would not work properly in my case.

To be fair, nothing broke, everything went together per measured specs...as well as by feel when I tried that after the measured stuff did not work. It just did not work.

PowerTrax was really good about helping me and eventually refunding everything despite my messing with the parts. I purchased through Summit by the way and they were great too.

With your drag race intentions I suggest you skip the "lunchbox" locker idea. Save a bit longer and get the stuff that will last, work properly, and have no special needs.

I run a Detroit Locker in my 7-LITRE Galaxie and it is a set it and forget it thing.
A bit noisy?...yup. Clunks into lock?...yup. Requires a little different driving style?...yup.
Locks every single time without fail?...yup. Gives any trouble?...Nope.

I have witnessed, as well as used, plenty of clutch style locking differentials and here is my thought on those.
In a stock, or slightly hot rodded engined muscle car running street tires (nothing specifically grippy) they work pretty well because the power is not there, and the tires do not grip really hard.

Once you modify to power above about 500lb/ft torque you will burn up the clutches quick.
Once you install sticky tires you will burn up clutches pretty quick.
Once you install a high stall converter you will burn up clutches pretty quick.

If you have a nice 9" Trac-Lok, 31 spline, behind a stout FE, running Drag radials, and a clutch transmission, you can burn up a clutch locker in three passes.

Unless the car is totally dedicated to drag race action I do not recommend a spool, or anything like that. They do get the traction, but they alter the driving style considerably as well.

Save your money until you can get the Detroit Locker, then put the rear end together.
For now, let the one rear tire smoke and pedal the throttle.
In the long run you will be better served going this route instead of some sort of compromise.

Brent: my set of completely original (greasy and grimy) VC's like that, have no stickers. I can't remember which engine/car they  are from. But certainly not a 428.
Cleandan: is that what an original air cleaner element looks like? Is that an original style air cleaner?
Richard

If your engine was equipped with the "low restriction" air filter housing the air filter looked very much like the one shown in the photo.
A somewhat creamy yellow, pleated element, orange foam encasing the ends, and a metal cage around the pleated element with circular holes.

The air filter top and bottom changed for 1966 and there were two versions of the same open element filter housing.
Chrome: Part of the engine dress up kit. This would have a chrome top with an engine blue bottom.
Standard" This would have both parts painted engine blue, otherwise the parts were the same between the chrome and painted versions.

If you look at places like Scott Drake, Summit, and others the chrome 14" filter housing they offer is usually the same basic design as the 1966 version...just crappier chrome and metal than originals, but often less rust than originals too.

Good day Brent. This appears to be a Galaxie 7-LITRE engine compartment, is this correct?
I have had mine for decades...still a POS, but I like it anyway.
When I got it things were very untouched...worn out, but untouched.

The round sticker was centered on the oil breather/fill cover top.
The air cleaner lid sticker was on the outer rim, flat area. Not on the inner portion like in the photo.
The service sticker was on the drivers fender well, on the outer side of the fuel hose, near the plastic clamp, about 1/2 way between being next to the clamp and the top of the inner fender curve, positioned as to be read from the front of the car, not sideways as if standing with your body against the front fender. But not perfectly aligned either. I was stuck in the general area with some care, but not critical care.
There should also be a round sticker, centered, on the brake master cylinder cover.

This photos I see the air filter lid wing nut is so tight it has bent the lid. For 1966 the lid top is flat, not curved, with a slight recess for the wing nut.
I see other things too but I'll leave that go.

I tried the Lock Right locker, from Powertrax, in my 1990 F250. This is my daily driver with a stock 7.3L IDI diesel and 3.73:1 gears. I figured with my marshmallow diesel, and ho-hum driving style, the Lock Right would be a perfect fit for my traction needs.

First, Powertrax was really good about helping me get this right. I eventually spoke with their in house engineer a bunch of times and I did all kinds of measurements, fittments, and so on in an attempt to get things just right. Everything measured correct.

In the end I tried two different Lock Right lockers, as well as measuring and combining parts from all of them, to get the best fitting, most correctly measured set up.........And it still would not work properly.
I got really good at taking the thing in and out, so I got that going for me.

Finally the engineer admitted that some differentials just don't work well with the Lock Right and my Sterling 10.25" was one of them.

The problem was it acted like a spool, with ZERO differential action, and this made the truck drive...well, not properly.

I think the Lock Right can be a good alternative for getting better traction, and they seem to hold up pretty well based on what other people have experienced, but they are a lesser locker than other alternatives.

I eventually installed a Yukon Grizzly Locker (a more durable Detroit Locker) and have been very pleased with the set up for the last 70,000 miles.

I didn't try to boil race gas, but it solved the problem I was having.  I eventually went to a return style fuel system on the car, and re-routed the fuel lines to keep them away from the engine as much as possible, and that solved the problem.  FYI the fuel was 92 octane with 10% ethanol.  Race gas would certainly boil at a much higher temperature.

New cars don't need to worry too much about the boiling point of the fuel, because with direct port injection used on new vehicles, the fuel is under pressure right up to the point where it is injected into the engine.  45+ pounds of pressure raises the boiling point significantly.  The problem I was having was a heat soak issue; I would stop the car, the fuel lines would get hot as the underhood temperature went up, then when I started the engine again after about 20 seconds the hot fuel would go through the needle and seat, lose pressure from the fuel system, boil, and spit out the carb vents, flooding the engine.  Took me a while to figure it out, it seemed like the engine was fuel starved, not flooded, but finally one day I duplicated the conditions while the car was sitting in the driveway, and watched it happen.  The amount of fuel spitting into the carb was rather remarkable...

This sounds like a great job for a GoPro camera in the engine compartment.
I know the fuel is evaporating due to heat soak, and boiling when the engine is shut off because the fuel pressure drops...This is plain science at work and there is not much I can do about it.

I never thought about the fuel boiling so violently that it would erupt out the vent tubes.
Currently I have the floats adjusted so the fuel is just barely at the bottom of the view port threads when slightly shaking the car to check levels.

I wonder if lowering the level a bit more may help. I will know, due to fuel starvation and the engine losing power, if I get the level too low.