The easiest way to tell if you have the late floor pan in the access holes location for the shocks. If they are on the top it is an early style if the access is at the rear for the shocks it is the very late pan that is much the same as the 1972 pan. In 1971 Challenger had three different types of bumpers for the front and two different for the back. My Challenger has the slotted bumpers both front and back.