They will swap. Only difference is where the lights are. On a 71, the lights are mounted below the bumper, so you will need to acquire those lights, and they are sorta rare. Sorry Dave. I remember being a feisty young chap like him... That was, what...6 months ago???
Why do you want to change it? Is the 74 grill broken? Also if you have the big bumpers you are going to have to get a grill from a 73 and up (or a LDO or Grabber) the standard 69.5 to 72 did not have provisions to mount the turn signals in the grill. The LDO and the grabbers had lights but they are kind of cheap fog lights, the directional lights are mounted under the bumper in the lower valance, that the later (big bumper) cars don't have
idk my grill seems kind of cheep, plus i like the look of the 70 grill, sorry i messed up the years, i have confermed that i like the 70 grill anyways, i hate my bumpers too, they are tooooo big!