50GMC253-

I agree that the ports are in the carb base, but if you bolt the carb right to the manifold, the surface of the manifold will cover the ports. The spacer has "notches" cut out in it to open it up for manifold vacuum.

-Tim
'51 Chevy 3104 w/'56 235, 848 Head, HEI Dizzy, Corvette Cam, Split Manifold and Dual Carter YF's