Open chamber 318 heads are not even worth their weight in scrap iron. If they are closed chamber heads like the 920 or 302 they can give average 70s and 80s motors a bump in compression and the 302 head is good for MPG motors because of their high swirl charicturistics, even then they are not worth a lot. The older 315 casting 273 heads are small closed chambers also but need early 273 intakes to match the intake bolt pattern. There is at least 1 other early 273 casting but I can't remember the number. Also the 714 is a really late 318 head just like the 302.