Catalytic Converter on a 65 Slant 6?

I would NEVER "add" a cat to anything unless smog requires it and under certain conditions they can generate dangerous levels of heat and create smell on their own

Check car for leaks. ANY leaks through holes gaskets etc into the floor and trunk of the body are suspect. Leaks in the exhaust are suspect

Be diligent about checking that the timing is actually where you think it is, and re-check your idle mixture settings. If you can not kill down the idle speed by turning in the idle mixture screw, then there is something wrong getting too much fuel into the engine.