Pull out all the spark plugs. Spray some PB Blaster in each spark plug hole, working it around to soak the heck out of each cylinder. Let it stew for a coupla-few days. Then try to turn the engine over by hand using a socket and breaker bar. Hopefully you'll be able to break the rings free and get it turning over. No guarantee on the condition of the cylinder walls. You might wind up with an oil burner, you might get lucky.
Here's another thought, it's possible the starter went out and the bendix gear got stuck in the flywheel. That can give you the impression that the engine is seized when it really isn't. I'd actually check the starter first, but soaking the cylinders and working it in still would be a good idea, even if the problem is with the starter.
393 Stroker, Tunnel Ram, Dual Holley's
"I only live for today, but I'm one day behind"
Eats Rice and Poops Out Fords.