273 "commando"

65 4bbl had a pop-up piston, it was a pent-roof design so it fit into the 080 head I assume as the chambers were 'closed' per val and mike. If you can see 2 valve reliefs through the spark plug hole, your looking at a 2bbl piston. If its smooth on the plug side, its a 4bbl piston. Good luck on seeing them though.