Need advice on used engine

I think the heads should be almost identical between 66 & 70. Both are "drool tube" type, i.e. removable spark plug tubes w/ rubber seals. The seals are cheap, so no reason to drool. Much later heads (~1976?) had integral plug holes, with the disadvantage that you can't remove the lifters without pulling the head, so a camshaft swap is tougher.

If the spark plugs are protruding more (sounds like), the PO might have left the metal gaskets on. You are supposed to remove them. That puts the plug deeper in the head for better spark plus a little more compression. Of course the plugs could just be a different PN.