Have you actually tried what you say can not work? I have run a 273 with 72 340 J heads. Best it ever ran, and that is with a 3.665 bore and 67 cu in smaller.
I think we're talking about 2 different things. 273/318 heads are about 60cc and 360 heads are about 72 cc's which just makes very lo compression in a small engine.... and yes I know guys that run this combination.I'll say no more.
We disagree, it's OK, i'll stick with 340's
