These really aren't prone to self destruction. They have some head gasket issues. Occasionally a head or push rod. I personally would confirm if the piston still did its up and down thing and determine how bad this is. Did the crankcase oil get contaminated w/ fuel or sump run low?
If it did go away, I'd look at some of the online wholesalers for a complete before making a decision.

Ron, Same problem here in SE Virginia. ~250 hours and the engine seized while my son was mowing this afternoon. Tell tale sign was found after removing the spark plug to relieve all compression and found the plug lead was mashed against the plug and twisted to the side slightly. Did you find a replacement engine or repair the one you had?