318 block/340 heads?

That would have been used if you needed vacuum to run to your int and operate your heater and defrost selection in newer mopar cars if needed.
Pull the vacuum advance hose and plug it off, I would check the base plate and gasket under the carb for vacuum leaks , spray W-D40 around it while it is running and see if the engine revs up and smooths out some, It could be just a gasket leak there.
I don't see a thick gasket under your carb, A good way to keep the gas cool.