V-8 flathead problems

[BCA]

I'm getting an older restoration F15a running after it sat for a few years. I can get it to idle fine but there is no power above the low speed idle range. When I floor the pedal it just coughs and the only way to get it driving is to use very little gas pedal - obvious it won't go very fast. It gets worse as after about 15 minutes of 15-20 mph driving.
I have tried 2 carbs: the original and a rebuilt one. Same problems.
The spark is good (tried another coil just in case heat was a problem). I've changed the fuel pump (2-2.5 psi pressure) and also used an electric pump in line to be sure of good fuel delivery. Fuel is clean and fresh and lines are clear. Working the choke does not add to performance when trying to baby it along above 5mph.
My only guesses at this point are: bad ignition timing, spark break down at higher revs(divers helmet distributor, points look clean from what I can see with the 2 caps off - I have no idea about timing it) or high speed problems with both carburators. The rebuilt carb was professionally done and looks good. I looked for errant sparks along distributor wires when it was dark: no obvious shorting
Spark timing or Fuel? Any suggestions? .... Brian