The clear bra for the front is a great idea. They're computer-cut and they do a terriffic job.
I wouldn't bother buying any extra parts, especially based upon supply/demand of those parts for your 71. An OEM 2015 grille, and the desirability of it down the road, has nothing to do with supply/demand/desirability of an OEM grille for the 71.
Dealer will sell color-matched touchup paint and clear.
I wouldn't undercoat it, and in fact, if you do, you'll void the OEM corrosion warranty in many cases. Cars are much better built to resist corrosion now than they were back then.