I bought a project truck and the guy who sold it to me wasn't sure the motor would turn. I can't get it to turn by hand for certain, not sure if I can even figure out how to get a socket or how big it would need to be.

I am looking to get going on this project after a VERY long delay. Any ideas on freeing this motor up and how to make it turn would be welcome.

1948 dodge power wagon. 215 motor. It was rebuilt in 1955 according to the tag on the block. That should be recent enough...