Was this stored outside in the elements? in a car outside? In a shed or something? I would pull the valve covers and make sure the valves are not stuck. lately that seems to be what I've found for issues with stuck engines.
Excellent point. Never get so locked into trying to solve a problem that something simple and obvious is overlooked. It is kind of like spending hours tracing the cause for no brake lights only to find it was a burned fuse.