Slant 6 4 barrel carb

Fro driveability, a vacuum secondary would be the best choice for a smaller displacement engine; the engine will draw what it needs, not what the driver tries to force it to use. I assume this is for the street? Any cam upgrade? Other things being done, like new timing chain and bigger exhaust? If you don't riase the breathing power of the einge, you are very likely to be dissappointed.