273 "commando"

I wouldn't pull the head just to check the piston type. Buy a USB "endo-scope video camera" on ebay. I paid ~18 and has paid for itself many times. The head is ~1/4" D and easily fit thru an O2 sensor port (to view catalytic converter), which I think are the same thread as larger spark plugs so "should work". Has a built-in LED light. Plug into a notebook PC and use standard Windows accessory software that works w/ any USB camera.