If you are going for very correct parts - there are some differences between the 71 and 72/73 trunk lock.
From the 429 Megasite:
"Although the 71 and 72 Mustangs appear identical, there are some differences. One of them is the deck lid. Starting on 3/1/72, the 1972 deck lid part number changed from D1ZZ to D2ZZ. With this change, a slot for an exposed and pop riveted lock cylinder retaining clip was added .... The 71 deck lid ... does not have this slot. It has the lock cylinder retaining clip inside the deck lid sheet metal structure. It is thought that the 71 design, which required the assembly line worker to put his hand inside the metal frame work of the deck lid to install the lock cylinder retaining clip, posed an accessibility problem and possibly a safety issue (sharp metal edges). These issues may have lead to the design change in 72 with the much easier and safer slot for external installation of the retaining clip.
Note that 72 Mustangs built prior to 3/1/72 used the D1ZZ 71 decklid."