Sorry I'm late to this party; been buried in other stuff. In a nutshell, I'd stick with the cam you have if you want to power brakes to work reasonably, and I'd probably build a set of 1 7/8" to 2" to 2 1/8" step headers. Primary pipe length isn't going to be critical; shoot for around 30", but anywhere between 25" and 36" should be fine, and I also wouldn't worry about keeping the tubes all the same length; I think it is more important to get that straight shot out of the port for as long as possible, and then maximize the bend radius of the tubes. If you can afford a merge collector that would also be a good investment, and a long collector will help you quite a bit; the collector volume is quite a bit more important than the primary pipe length. If you are going to put mufflers and an exhaust system on the truck (I assume so!) put a crossover pipe at the end of the collectors, to effectively define the collector length.
I think Ross's numbers for HP and torque are probably about right, and bear in mind that a chassis dyno will give you rear wheel HP, while the engine dyno software will give you flywheel HP in most cases. So don't be disappointed when you get to the chassis dyno and only see 440 HP; that will translate to around 550 HP at the flywheel.
Looking forward to seeing the header pictures and the dyno numbers...
Thanks for your input Jay!
I would be happy with 440 at the wheels and 460 or more torque. Although for the $$ spent if thats all it makes would never do it again . .
I was just going by what my mostly stock 427 Comet did.
It made 420hp & 440 tq at the wheels on a 105 deg day with no tuning. Pretty much as I drove it to dyno.
Stock bore 427
Stock unported MR heads
9.6 to 1 comp
6113 Hooker headers
Good 3" exhaust with Dyno Max Ultra Flow mufflers, it did have a crossover.
It had a close to stock solid cam
Stock carbs and MR intake
Stock ignition etc
Again that was with a Top Loader so do expect more loss with the C-6
In the past I have done engine dyno then chassis dyno just to see the loss.
Pretty much all were a 100hp loss with a 4spd and 120 with a c-6 That was 500hp engines.
Looks like my dyno program is a bit HAPPY!
Its typical cool arizona day 1000' elevation, 72 deg temp with 12% humidity.
Typical for the PHX area
I am at 1966' elevation that by itself kills power around 25hp.
If I change the desktop dyno to 2000' elevation, 100 deg F and 30% humidity it drops the numbers to:
548Hp @ 5400 RPM
586 TQ @ 4200 RPM
It shows 438 RWHP & 469 RWTQ
Which is pretty much in ballpark to what Ross/Jay said
Again its just a bench race tool. The real dyno will give me the numbers . . .
I will be very very disappointed if it does not make 460 TQ to the wheels . . I did a LOT better with a Cast Iron D3 head in my 460 pickup . .