I don't have a very good picture in my head of what a 1966 Comet
dashpad baseplate looks like, but could you press on a veneer over the
bare metal of the whole thing? I guess you'd need to rough up and
carefully clean the surface of the metal and then use CA glue or
contact cement, or possibly gorilla glue (don't know how this'd do with
veneer). Or Rockler has PSA-backed veneer sheets up to 24"x96".
Sounds interesting - post a picture to APBW when you get done.
Good luck,
Andy