Best Carter carburetor upgrade for 67 383 s?

You could put a spacer under the new carb. I would not do that myself. I would ether do;

Bore the intake holes out for the larger butterflies of the larger carb

OR

Get a TQ intake and large TQ carb.

IF staying with an OE look, becareful of what carb you pluck from another engine. The early 440 engines did indeed come equipped with a small AFB.

Make sure you get the "750cfm" AFB or AVS, which would be my choice, AVS that is.
Rumblefish360

Thanks for the advice.

Carl