It quit under use? Have you removed the spark plugs and looked for damage to either plug, which could indicate piston has come loose.
This is OHV engine, I would remove the valve covers and see if a valve may have come loose. If valve has coe loose, you may save engine by pulling the cylinder head and check for damage.
1st call no answer, 2nd call no answer.? Did you check the spark plugs and there is no fluid on top of pistons> If no damage shown on the plugs, and engine will not turn, check the pulleys on the bottom of the engine, remove the belts, to be sure belt has not jammed engine. Then if engine is still locked, I like to remove the cylinder heads.
Good job. Not a common problem. Thanks.