In the glove box of my challenger was the Vehicle And Owner Identification paperwork. This lists the original owner's name, delivery date, Selling dealer name, account number, VIN, city, etc.
Delivery Date: 4-23-74
Dealer: Tecumseh Motors
Account Number: 65419
City: Tecumseh, Nebraska
A basic google search didn't turn up anything relevant (hindered by the fact that Tecumseh is actually a brand of motor).
Is it worth trying to track down the original dealer? Are they likely to have any records?