Assuming he wasn't a resident of your state, I'd call the ATF on both of you.
This was 35 years ago...Before the Constitution was illegally redefined and the 2nd was still respected.
Hocking Guns for repairs and such were very common place back then.
That doesn't mean it was legal.
Maybe it was not legal, but minor things like this were not really enforced back then.
Thing is...I was a Ca resident, He was moving to Ca to become a resident, and the temporary exchange happened in Ca.
Do you think they would have taken the time and resources to prove a difference? Even if someone called them they would have probably just disregarded it.
Towing and Repair was a pretty good gig for Firearm Collectors back then.