The '70-'72 Slant-6 exhaust manifold has an open hole where the choke thermostat goes (not the "pull off", which is up on the carburetor itself). In that hole sits a stainless steel cup, and on top of that cup sits the choke thermostat. There's a gasket between the cup and the exhaust manifold. If you are seeing smoke, that's probably where it's coming from. The gasket is no longer available; you will have to make or find one (I think I have
one left; send me a PM if you want it).
There should not be any smoke, though. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted
here for free download.