I have a '68 Chevy truck with a 292. On this, the heater plumbing is, in effect, a second by-pass, and the heater does OK. I'm more concerned with getting the all the air out of mine. Seems like an air-bubble trap to me. I guess a guy could go all crazy, and run his automatic transmission cooling lines through it. Heck, hot ATF might be a better media for heating the manifold up, anyways.
