Isn't that 390cfm a bit under powered for a 302? I have a carter 1406 that I think is closer to 500cfm on a Stud 289 as a comparison. I've also read that the fuel load from a 4bbl tends to pool a bit in the manifold on long intakes like a GMC has, which is one plus for a 2 carb set up as it has a wider distribution 'footprint'.
