Slant 6 hot running issues

It is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions. Install tech tips here. And if your exhaust manifold fails inspection (cracked, warped, gasket surfaces no longer flat, etc), see here.

And while you are at it, consider ditching the rinky-dink, cold-blooded factory choke setup for a № 1232 Electric choke kits, which—unlike the original, is adjustable (hallelujah, praise be!).