360 magnum

Before you pull the motor: Is it locked up? Does it turn over with a wrench or starter?

If it turns over why don't you take off the heads and put each piston at BDC, then get a 4" wire wheel on a drill and take the rust off of the cylinder walls. I bought a 75 valiant where the guy took off the passenger bank head and left if off for a while and the bores were rusted. I cleaned them up with a wire wheel, then carefully blew out all of the rust and lubed the cylinders with STP or Motor Honey and it ran fine.

Just because there is some surface rust on the bores doesn't mean the game is over for that engine.