the previous owner didnt know how to drive an automatic, and went to rev it in nuetral. well, he slid it up one too many and went into reverse, full throttle, while still doing 20 mph forward.

 

The same darn thing happened to a friend of mine back in my younger years. It was with a 65 Impala 327 powerglide. The tranny was fine, but the engine jumped time. We replaced the chain, and back on the road. Small price to pay compared to your previous owner.