An Old Timer once told me...

That was actually pretty common starting about 1974 for several years. The open chamber heads on a 360 were about 72cc and they dropped the piston in the hole for lower compression. A fast easy fix was to work over a set of 318 heads and bolt 'em on. along with a timing gear set. They ran better than stock by a bunch. The 318 heads could be bought as re-man really cheap around that time too. Maybe they weren't all they could be in high rpm but it sure improved them as a regularly driven street motor over the stock smog dog.