Better head

67 and down heads had a less efficient chamber design, 60-62 heads had looser control of the chamber placement in the casting except for the "special" or star casting mark heads intended for the aluminum block motors.

All 63 and newer heads have the tighter chamber placement tolerances and will work on aluminum or iron block.

All 68 and newer heads have the same chamber.

Drool tube heads are a little lighter than the late style heads but are functionally identical.