My Opinion is just take all the pictures to document what you have and what was there and rebuild it in as found condition. Only putting back and restoring what's there. It is a valuable car just because of it's heritage. No one can change the fact that it is an FC7 R/T SE U code 70 Challenger and just leave it as that.
On another note...
IMO also is that you found the way the internet works too...These threads always get crazy especially in winter. Now that you have "outed" the car that it does not have a tag or a broadcast sheet it will take a huge hit because by the end of this thread it will have been a /6 a/c 71 Challenger that has now been re-bodied and now highly optioned 70. I would keep the Vin number myself to prevent further tainting of the car and leave the fender tag missing...