That's a great price, you know thats only the "short block". You will need to take off all the external components off your old engine, like intake, exhaust manifolds, carbs., starter, etc, and put them on the new engine.
I also would get a local mechanic to look at your old engine before I made that jump. Maybe someone on this forum who lives near you. Start a new thread "local mechanic needed". You could have other problems other than the engine is locked. You might save yourself some money in the long run.
Lou