71's (except sportsroof and Mach 1) will have the block letters (Mustang) across the trunk lid, 71 sportroof had a stripe across the decklid with the Mustang letters cut out, but it often did not get replaced on a repaint. Taillights on 71-2 have a blackout pattern around the lenses. Front turn signals are under the bumper. Bemper can be chrome or urethane, depends on the options.
72-up (except 72 Mach 1) will have the Mustang script like the fenders on the lower right of the trunk lid. 72 was the first year of the "Fasten Seat Belt" buzzer, so all of them will have the lamp in the center of the passenger dash.
73 will have as mentioned, vertical parking lights in the grill, the big urethane impact bumper, painted hood/fender mouldings and the taillights are all bright metal, no blackout paint. There's also the rear bumper that sits out further from the body with filler moldings. 73 Mach 1 has the wide stripe just above the lower body line.
There's more, but those are the major items. Pick up a Mustang Recognition guide from your favorite Mustang parts store, it'll detail the differences between all of the years.
Last edited by Hemikiller; 07-23-2010 at 08:51 AM.