Not sure if it will apply to this particular motor, but if you're trying to get a look inside without tearing things down to far I have had success renting a flexible inspection scope. Some have a light built in and some don't, if you don't have a light on the end of it it makes things harder (trying to juggle and aim a really bright flashlight down the spark plug hole is no fun). I would think that if it were a head gasket there would be some oil dribble from the head or heads, unless the motor was super dry on the top end (or already covered in oil to the point where you can't tell if it is leaking). using a flexible inspection scope and very slowly turning the motor by hand (if it still spins) should help to get an idea of what's going on. It helped me find a broken rod on a dormant Benz motor years ago, was better to find it that way than to try to start up without knowing.

62' GMC Fleetside 3/4 ton 235 4-speed.
Time makes fools of us all.