See if you can do a title history on the car and that should give you a large clue as to who owned it first.

carfax is a bust :(

Date: Mileage: Source: Comments:
05/21/1985 NICB Vehicle manufactured
and shipped to original dealer

11/04/1991 45,834 Utah
Motor Vehicle Dept.
Marysvale, UT
Title #5043784 EXCEEDS MECHANICAL LIMITS TITLE ISSUED

CARFAX Advisor™
An EML title is issued when the owner discloses an odometer rollover to a DMV. Rollovers occur on vehicles with 5-digit odometers that go from 99,999 to 00,000 every 100,000 miles.

Mileage reported after this reading is potentially unreliable.
11/05/1999 Utah
Motor Vehicle Dept.
Enterprise, UT
Title #9188152 Title or registration issued

^^ My registration

EXCEPT there was only one other registration before ours. Does the state not register vehicles? ('85-'91)

That's a good starting point, with the second owner's title number on there. Most cars that came out of service have similar Carfax reports. On face value, it looks like your car was in-service from '85-'91.

Mike, what can I do with the other title number?

http://www.dmv.utah.gov/privacy.html
For use in research activities and for use in producing statistical reports, so long as the personal information is not published, re-disclosed or used to contact individuals.

Like Matt suggested, you can try a title search. It depends on Utah's laws/policies for record storage/release of info, but you may be able to find the person who originally bought your car at auction, for research purposes, using that title number. Some states keep copies of the original titles on microfiche, and you also may be able to find the title number (or a copy) of the original title from UHP using that second title number.

EDIT. Brian beat me to it. :)

Brian, that is awesome! Thank you! You guys are the best, thank you!

That is what I did with my '86 FHP, found the owner who bought it at auction.

Utah does not mention anything about a cutoff on the years going back, it's worth a shot either way.

Also, I pulled the bottom back seat out and lifted the carpet this afternoon, and the little plastic "pouch" that I assume held the build sheet was empty. Oh well...

No pouches that I have ever seen. Have you checked behind the rear trim panels? (the ones on either side of the rear seat, with the built-in armrests) I have found 3 in cars, taped up on either side (driver or passenger, inside the trim).

Here is one from the buildsheet section on the site, still taped in place when I found it.

http://www.specialservicemustang.net...82chpbuild.jpg