Found some documents. The Protecto Plates are still there. The engine number matches and this shows it is a 4 speed car from Oldsmobile.
Also found a document that confirms the original owners story. He said he had just had a muffler put on it before he parked it. This document I found shows that he got the muffler in July of 1970 with 88224 miles on it. It was last plated in 1971 with 90,000 miles on it.