Can't argue with your results, but I can say, having ignition control makes it significantly more adjustable and can make it better

I have heard of the dual plane issue, but haven't seen it.  That being said , I generally notch the dividers anyway with a dual plane, so it may be why.  However, assuming the IAC doesn't make a vacuum leak on only one bank, it shouldn't cause an issue, but I have heard it.

As far as LSA over 110, doesn't compute for me, every single EFI engine I do is over 110, (my Mustang is 110 LSA, 72 degrees overlap but also Mass Air Flow equipped) but LSA alone doesn't matter much, it's really how much overlap.  I could buy a typo that excessive overlap for tighter LSA could screw with idle due to unburned fuel in the exhaust, but not greater.  Would be interested in what you saw on that.

You make a valid point though, 50% of the builds I do are carbureted with standard ignition curves and they do great.  However, so does EFI, but once you start understanding the programming, you can do magical cheetah flips with timing and mixture in a variety of situations with EFI.  Do you NEED that?  Not necessarily, but when you do, it's real nice.

Don't get me wrong though, I agree on your experience, 1200 bucks worth of stuff, maybe 2000 when you add ignition, plus more high pressure fuel changes.  Someone really has to have a desire or need, if you don't, it's a lot of money

IAC Hold is where the IAC parks once you give it throttle, if it's too high it won't idle down easily

Ramp Decay is the time it takes to relax from the hold point once the throttle returns

RPM above idle is where it starts to settle

RPM above idle to start idle control is when the IAC takes over actively, not the ramp down

I think your idle speed to start ramp was high, and you went higher. That will essentially ease the idle starting at that point

However, logs are your friend, going to need to get that working again to really figure it out

I run an early Pro-M on my Mustang with some significant modification and a Pro-flo on my truck.  Both do great, the Pro-flo is more  fancy gadget than performance oriented and didn't fit well.

That being said, every one I do for a customer is a Sniper now or Terminator X if port injection.  2 last year, a 511 FE and a 347 SBF on the stands now.  Holley has great support, nice website for getting help, easy and intuitive handheld or laptop connection, and gives you a lot of alternatives when growing into it.

I like the Sniper Stealth for a TBI for looks, recommend you get a matching distributor, Hyperspark or DUal Sync, and if you want port injection, build it in pieces and drive it with a Terminator X box.

Happy to offer more detail

Nothing to say about FAST, FiTech but they don't seem to have the following of the Snipers

I have a 428CJ "C" scratch numbers matching engine that I just bored to +.030" over, and did a fresh sonic test that has cylinder walls capable of +.065" overbore and still have at least .125" everywhere.  The block is dated 8G23 which should be a '68.5 dated engine.  I believe that those real CJs have decent cylinder wall thicknesses remaining if the owners used antifreeze in their engines from the beginning.  Joe-JDC

I sonic check a few too and the C scratch is almost always head and shoulders over the early X, A, CI, and CX in thickness and consistency.  The later CI/CX can be as thick, but often inconsistent in core location, X and A tend to be a little thinner.  I agree with you though, if everyone would have used good antifreeze, things would be much easier.  I had one Mexican 302 casting that was thick for a Windsor, but rusted from the inside, sonic checked good, but I poured a little gas in the water jacket because I saw a shadow and it weeped.  Pitting can be bad

A flow bench does all of it's work on the chamber side.  When flowing exhaust you reverse the flow and open the exhaust valve, so there would be no way to have it push on the exhaust and suck on the intake at the same time

However, if you did want to optimize, you could chase low lift flow on the intake side, I am no porter, but that doesn't always help higher lift.  Best is to have a port that is clean and not too much volume

On edit - here is a cleaned up video from the owner

Glad he could, it is a pretty engine

https://www.youtube.com/watch?v=mtgO0UFeXIA

Too funny! Special cam stays open 10 times as long, more power!

Performance Summary:
      Cubic Inches:  457             Dyno brand: Stuska
      Power Adder:  N/A             Where dynoed:  Dale Meers Racing, Buffalo, KY
      Peak Horsepower:  528@5900
      Peak Torque:  555 @ 4000


Engine Specifications:
   Block brand, material, finished bore size, other notes:  1969 C scratch 428, 4.150 bore, CnC squared, aligned, torque plate honed
     
   Crankshaft brand, cast or forged, stroke, journal size: SCAT cast 4.25
     
   Connecting Rods brand, material, center to center distance, end sizes, bolts:  SCAT I-beam 6.700

   Piston brand, material (caster, hypereutectic or forged), dish/dome volume, static CR: Racetec, 14 cc dish, 10.03:1

   Main Bearings, Rod Bearings, Cam Bearings brand and size:  Clevite rod and main bearings, Durabond cam bearings

   Piston rings brand, size, other notes: Mahle 1mm/1mm/2mm standard tension

   Oil Pump, pickup, and drive:  Melling M57HV, Canton pickup, ARP drive

   Oil pan, windage tray, oil filter adapter:  Cobra aluminum repop, no tray, factory oil filter adapter

   Camshaft brand, type (hyd/solid, flat tappet or roller), lift and duration (adv and @.050"):  Custom Bullock's Power hydraulic roller, 237@.050 intake

   Lifters brand, type:  Morel standard travel

   Timing chain and timing cover: Cloyes 9-position roller, Roush alum timing cover

   Cylinder heads brand, material, port and chamber information:  C8OE-N CJ, Les Schmader ported, 3/8 unknown aftermarket undercut stem valve, 2.09 intake, 1.67exhaust, Viton seals, ID spring locators

   Valve springs: Crower 160/420
 
   Rocker arm brand, type (adjustable or non-adj), material, ratio:  Factory nonadjustable, 1.73

   Rocker shafts and stands, brand, material:  Harland Sharp shafts, Trick Flow studs, Precision Oil pump end stands

   Pushrods brand, type, length:  Custome Smith Brothers 5/16, 3/8 ball/ball non-oiling

   Valve covers, brand, type:   69 CJ aluminum

   Distributor brand, advance curve information:  Pertronix billet, 38 total

   Harmonic balancer brand:  Stock, restored

   Water pump brand, type (mechanical or electric):   Tuff Stuff aluminum- electric powered on dyno

   Intake manifold brand, material, porting information:  Blue Thunder CJ, with divider notch cut

   Carburetor(s) brand, type:  750 dyno carb, but engine will run a Terminator Stealth

   Exhaust manifolds or headers brand, type:  Dyno headers