[Gromit]

One thing I notice about the fuel supply setup (and I may be wrong in thinking it is not optimal) but that loop of fuel supply hose is higher than the height of your carburetor and fuel bowl - wouldn't that encourage the fuel level to fall back inside the hose each time you shut off the motor and maybe create a vapor lock?

Autozone sells the vacuum caps in assorted sizes (photo attached)

One unrelated thing I notice from your photos is running the single accelerator return spring risks it suddenly breaking and the accelerator sticking open unexpectedly.. the double springs are just a few bucks - usually on the wall at the big box stores in the "Help" section..

Also maybe someone mentioned this already but that vacuum canister looks suspect - their operation depends on a rubber diaphragm inside and they do get pretty baked by engine heat over the years - it would at least be worth checking if you have a vacuum pump like a Mityvac or similar.