Since the discussion morphed to fuel issues, I'll add that I think the Carter BBS carburetor is easier to trouble-shoot than the Holley 1920. It was used on early slants (my 1964), but perhaps only with the rotating throttle rod rather than a throttle cable. Like the common BBD, the BBS uses a metering rod to richen the mixture at high throttle. You can remove the top to verify actual fuel level. You can do that in the 1920 if you remove the "Economizer" on top and stick a wick probe down. The Economizer is akin to the "Power Valve" in 4 BBL Holley carburetors, and both are like the Carter metering rod.
The 1920 has several places to leak fuel, from the side-mount bowl cork gasket and from a torn Accelerator Pump diaphragm. The later can be hardened by ethanol to tear. With the hot exhaust just below, a fuel leak can be bad. But, worst issue is poor idle due to a clogged metering block. If you could source the 2 BBL manifold (Super-Six package of late 1970's) to use a Carter BBD, that would be great, but likely a goal for next-guy.