Alternatives to "M" code manifolds?

A few years back, I was talking to someone whom has a wealth of cross fitment knowledge having managed a parts counter at a dealership for a couple of decades who told me there are certain "C" body HP BB manifolds that can be "slightly" modified to fit into a 67-76 A-body.

Unfortunately I've lost contact with him and cannot ask him directly. I'm not pressed for this nor actually considering it at this time, but it sounded like it could be possible if someone was dead set on cast iron.

Thoughts?