If it doesn't turn over EASILY AFTER PRIMING IT to protect the crank & bearings, I'd just yank it out.

Personally, I WOULD pull it out, take the head off, if rusted, drop the crank out the bottom & knock each piston down a little, clean up the rust, then push the pistons out & see what you have. More often than not they need very little replaced, very rare to see mains & bigend bearings worn out, the cam bearings go first more often.