RE: 1970 Challenger R/T build sheet location
here is a few places to look. i just went through the same thing with mine. found one for a convertible and my car.
-Taped to the back side / top of the glove box insert.
-Under the front bucket seats in the springs
-Inside the bucket seat backs
-Under the rear seat bottom
-In the rear seat back.
-Under the package tray(speaker shelf)
-Under the carpet