Really rare to find a dealer that retains info, especially over 50 years. Even fewer that might transfer files to a new dealership owner.
Best bet is the individual state's DOT, although it sounds like AZ will not make the effort anymore like a lot of states. We were (and hopefully still are) doing the title and records search in TN; privacy laws forced our DOT to redact owner's names from the copies of what they have on microfiche years back - fortunately for us they still gave (sold) you the copies. I documented my two Z's this way - dealer invoices and MSO's, plus a complete tite history were on file for both cars (the important part: both were originally sold in TN, therefore they kept everything on file).
Good luck - it's a lot more difficult today than 20-30 years ago to track paperwork down, even with Google/internet search engines and everything else. If only Chevrolet had followed Pontiac in their documentation trail, we'd have a lot fewer fakes and bogus stuff going on.
Regards,
Steve
