1971: Sportlamp grill available only on the Mach 1, Boss 351, and Spring Special Coupe. All other 1971 models came with standard grills.
1972: Sportlamp grill available only on the Mach 1, Sprint Edition, and coupes/convertibles ordered with the Decor Group. All other 1972 models came with standard grills.
With exception to the Boss 351, all 1971/72 models equipped with the Sportlamp grill also received the urethane bumper.
All 1973 grilles went to vertical turn signals due to the increased bumper size. Two grills were available; a base version with a eggcrate pattern and a "corralled" pony, used on base models. A second honeycomb grill with a floating Mustang on tri-bar (the "Deluxe" grill) was standard on the Mach 1, and was (don't quote me on this - I'm a bit fuzzy on this bit of info) either an option on all others, and/or was included automatically if you ordered the Decor Group.
-Kurt