Yes they'll fit, but it will cost more than just the tail panel and front end.
The wiring will be a little different because the 71 has more headlights and the lights in the front valance, as well as different side markers. You'll need headlight buckets along with all the goodies to mount the headlights.
If you just want to put a 71 grille in between 72 fenders, it's possible, but requires either nip and tuck on the grille, or a new header panel.
If you're going to change the quarters, tail panel, front fenders, header panel and front valance then you still need the marker light kit along with the headlight kit, valance kit, and wiring for it all.
If you're not changing the quarters, then markers change between 71 and 72, so you'll either need to patch panel the quarters so the markers match the front fenders, have 2 different styles when you're finished, or delete them all together.
The bumper brackets are slightly different as well and would need to be changed out for 71 style so they line up with the dips and wiggles in the 71 grille. I'm sure I'm forgetting something, but that's a quick list of what you'd be getting into