What would it cost to go back to the original carburetor and manifold? A lot less than buying another incorrect carb, I'll bet!

At 5000 RPM and 100% volumetric efficiency (both of which are never going to happen) that engine will only be flowing 361 CFM. A 4 barrel of any sort on a Chevy inline six is a solution to a nonexistent problem.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!