1st: good luck, always like to see home-made projects go forward.
Light retainers, meaning titanium? or aluminum?
What cam LSA?
3,000 stall is whose rating? If it's based on a V8 with PG you'll have substantially less.
IMHO the manifold is small for that RPM range, which means an open spacer is probably faster. You can try 2 × 1" tall (if you have clearance). I'd remove the wall separating the secondary barrels, and blend the bottom of the bore cuts into the plenum interior, 3/8" radius or as big as you can.
Remember that your pump shot has to go up with a big spacer, possibly MJ also.
If octane is high, you want at least 15° initial spark lead (remainder in the curve, all in by 2,000 to be sure it's working when the converter flashes) before you do any idle adjustments to the carb. It's important that you not be above the idle circuit for staging, or the PV may open. You won't know the correct PV until your idle is sorted out, 2" below warm idle in gear is a good start (10" vacuum at idle, use a 8.0" PV). Remember, this determines only the timing, not how much fuel is added.
Because of the huge 1-2 RPM drop, you might find that the spark total that gives the best launch and 60 foot time is not as fast MPH as retarded by 2-3°. You can trick an electronic to retard in high gear with a solenoid on the shifter.
