[bubba327]

Pull the intake and exhaust manifolds and clean things up. There is a heat riser passage that allows exhaust gas to circulate up around the intake around the carb base if the bi-metal heat riser is working. this carbons up and needs cleaned out. the heat riser also rusts up and will stick open , closed or somewhere in the middle.
There should be three bolts connecting the exhaust manifold to the intake manifold., Sounds like you may have some missing or broken hardware.

The intake manifold can be changed to a clifford or offenhauser intake, but they should have hot water jacket cast into the bottom especially if headers are also installed . The inline six can be cold blooded with out the two manifolds working together, But the reverse can also happen. the fuel can boil out of the carb in extreme heat of summer.
P.S> the gasket is there to prevent the exhaust leak that you have now
good luck
The gasket shown in your first post is the correct one. But if you get the intake/Exhaust block gasket kit , It comes with a new base gasket and a exhaust doughnut plus a solid gasket for LPG applications(between the two manifolds)