The "easy" way to do it is to mount up some '70 fenders. This gives you the headlight buckets. You can also buy the headlight mounts from B/E&A, but they aren't cheap! I've managed to source some used ones, but all said and done I spent almost as much as I would have with new ones, although I got the entire front bracing from the fenders. You'll also need the header panel out of a '70, they're different than '71's (and '72-'74 of course). You may also need a new hood latch and support, they're different too. Also keep in mind your bumper set up is different, the '73 bumper sits further out from the grille. Then you'll need the headlight trim panels as well, keeping in mind the profile on the trim will not match the hood.
I still intend to swap mine to a '71 to match my wide hood and fender moulding. At this point I think I have almost all of what I need, but I spent a lot more than I thought I would need to, and since I still haven't mounted it up I may find I'm still missing some things...