I use a single 4/barrel on my racing 311" GMC. Technically the GMC and Chevrolets 6's are an odd fire if you count the pulses between the shared intake ports.
The real key to a good running engine with any of the combinations using carbs is a good consistant vacuum signal. I set quite a few records with a single Braswell 2 barrel which flowed over 700 cfm on a tube manifold which was not same length to all ports. I went to the 4/barrel when I figured out how to use a 292 Clifford manifold on a GMC 270 "H" head.
The additional venturis mixed fuel better and the factory taper of the Clifford increased the port velocity at the valve so I made more power. Next I will trying a Precision Engineering hi-rise manifold off a 292 as soon as I'm done with work..
The other key is to warm the manifold by using exhaust or water..Good Luck..#35
