Do you get the "Mopar Collectors Guide"?. If you don't, pick up the last 6 issues or so. Mopar guy, Galen Govier is holding on to hundreds of build sheets that he has collected over the years that have gotten seperated from there cars and is now publishing them in the mag.. It is a long shot but I have been looking for mine there. You can also have them post your sheet as missing in that mag. and on this and other websites. You've got nothing to lose buy this sort of research and who knows, you might get lucky.
That being said, my `68 Road Runner didn't come with any documentation, was also a gutted rolling old race car(JUNKYARD DOG) and here is what I was able to figure out just by taking it apart and restoring it. 383, 4spd., no power steering or power brakes, L1 turquoise with a black bench interior, 26" radiator core support, which meens it had the heavy duty axle package which included a 3.55 sure grip and a 26" radiator and a shrouded clutch fan, dash and firewall have all the correct cut outs for a.c. and it has tinted glass. Also likely had the decor package because of the large tin accross the trunk lid. I have actually found evidence for all of this info just by the restoration process and I still wish to God I had the fender tag and build sheet because what a great list of options this car seemed to have. Check out my photo galleries to see what I started with. If it was a race car, try and find out where it was raced and if anyone knows who owned it, they might be holding documentation on the car, or the people before, find previous owners. I have found out mine was raced in north Florida and have actually talked to someone that knows someone that recognized my car, still following that leed. Nothing to lose right?.