[NeighborsComplaint]

Verify that your choke is working properly. It's usually something simple. The choke plate should close fully on cold start and immediately snap open about 1/2" immediately after starting. The vacuum break that does this is internal. All you have to do is loosen the choke element cap retaining screws and rotate the cap clockwise for more cold enrichment (less gap) or counterclockwise for less (more gap). There is also a small adjustment screw that faces straight down in between the choke housing and carburetor body that adjusts the cold idle speed.

A leaking base gasket isn't going to foul your plugs and you already ruled out vacuum leaks with 11-1/2" of vacuum with a big cam like you're running. A vacuum leak will lean your carburetor out and would have to be massive to effect the power valve operation. You would have lean (gray) plugs at idle and momentary over-enrichment when going to full throttle all the time.

You don't have a (lack of) fuel delivery problem as others have suggested unless the car is bucking running out of fuel at full throttle. Part throttle blasts around town aren't going to tax all new components, even if they are stock and have 5/16" fuel lines. Your pickup, lines and pump are brand new, not 50 years old. The too-high pressure from the Holley mechanical pumps is pretty well documented and an inexpensive regulator is probably what is needed as the fuel pressure is lifting the inlet needles off the seats due to higher than normal fuel pressure. This will flood and load up your engine at low speeds where your fuel demand is low. On full throttle, engine demand compensates for the overflow.

I could go on and say your carb has a 6.5 power (enrichment) valve and a 5.5 would be more appropriate with your engine vacuum (and would probably clean up your idle and gassy smell), but it's not a big issue and is borderline. It's something you can do if you find no other cause. I run the 5.5 in my 750 with 11" vacuum. With the 6.5 power valve (factory setting), the car started and ran fine but just smelled gassy when driving..