Sorry TripGreen I won't be much help. I have read a couple threads on this site and it sounds like checking with the DMV could help but don't count on it. I've heard their records are limited for old vehicles or that they will not release the information. Going back through the person you bought it from may be a good starting point - beyond that
I'm more of a 'Cuda guy than Challengers so I'm not up on all their registries but Galen Govier runs the Chrysler Registry
http://www.gvgovier.com/registry.htm I've seen folks selling cars with letters from him stating how many are known to exist for certain option combinations. You may have to register your car to find out any info - again
Hopefully the Chally guys can be more helpful. Good luck.