Holley 500 CFM 2 Barrel #0-4412S on a Slant 6

That's a cool 2.2. ....I don't know. I've always preferred my carburetors a little big than a little small. I think carburetor companies tell people a little small is better because they figure most DYIers caint tune a carb, so small would mean less carburetor returns. I've always found there's more room to tune going down than going up. I mean all a 650 will flow is 650. But you can easily tune one down by leaning the jets and drilling out the air bleeds.