According to the 71-72 (and 73) Mustang Body Assembly Manual, page N-700-6, the bumper is the same as the one used in 1967, C7ZB-6362426. The 75 MPC has a C6ZZ-6362426-A for a replacement for 65 and on. To further complicate usage, NPD states that "70-73 used 2 different styles indiscriminately". In the manuals, the 66 style is shown shaped like a boot, the 71-72 style is shown as a round disc, almost like a hood bumper.
Jim