One of my thoughts was to use my differential pressure tester I use to do compression testing on aircraft. The thought was to rotate the engine until an intake valve opens then block off the carb, add pressure to the cylinder and check the crankcase for pressure. The only thing is how much pressure would you dare put on it.

1941 Chevy
"First rebuild - complete!"
Follow the story in the DITY
1941 GMC resting peacefully
1946/1947 Chevy Street rod on s10 frame complete
1945 GMC panel truck in line for restoration
1941 Plymouth stock complete
1941 GMC COE in restoration process
Read his Project Journal
1941 Chevy Coe uncertain future resting now