These covers are in the rear wheel well area, as you look at the front of the rear wheel, you will see this plate, it's about six inches up from corner of frame. it is mounted by four screws. Sometimes you have to remove the black undercoating to remove them.
These are exact reproductions of the OEM product. The 1963-1982 #3 Body Mount Access Covers include Screws. Sold as a set of 2, a left and a right side.