That engine looks pretty repairable to me. If it doesn't have any bits and pieces sticking out of the side, a repair is probably more feasible than trying to do a swap for an engine that you don't have any idea what's been done to it in the past. Try soaking the cylinders in a 50/50 mix of acetone and automatic transmission fluid for a few days (both on the shelf at Walmart) and see if you can free it up. I like to use the chisel shaped end of a shepherd's crook wrecking bar on the flywheel ring gear teeth at the bottom of the bell housing to persuade a stuck engine to move. I've resurrected quite a few engines that way, at least enough to run a little and see if they're worth rebuilding. My email address is in my profile information- - - -sending pictures that way works well.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!