Easy question!

When placing an aftermarket (or different to original) carburetor on an engine REGARDLESS OF BRAND, ALWAYS USE THE CARBURETOR MANUFACTURER'S SPECIFIED GASKET!!!!!

For Carter type YF carbs used on early Chevrolet 6 cylinders:

Carter 1A-24 (use with governor only) 788s

Carter 1A-31 788s (w/o governor), 789s, 966s, 967s, 2100s, 2101s

Carter 1A-41 756s, 787s (w/o governor), 964s, 965s, 2008s, 2046s

Carter 1A-59 (use with governor only) 787s

Using these gaskets will assure that the carburetor gets all the vacuum it needs. Next make certain that the specified gasket will not leak vacuum externally on the intake (or spacer).

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop