VIN Tracing Mr. Norms Cars

So, I just bought the 1971 Demon that my Dad bought new from Mr. Norm's Grand Spaulding Dodge. The engine is long gone to a mishap when he was racing, paperwork has been lost over the years to prove the dealer he bought it from. Does anyone out there know the best way to track this back to have paperwork proving its origin? We have confirmed 100% that it is his old car, but now need a paper trail. Any help would be greatly appreciated.