Tom. For starters, here is a link to MikeD's website for a new purchase, along with tons of other stuff.........and hands-down has got more information than you will need. Am outstanding site that honestly is 2nd to none. (
http://www.panteraplace.com/page58.htm)
On the cooling upgrades side, the radiator fans seem to be the biggie. The (2) stock pusher style fans.......one may be a 10-blade, the other a 4-blade don't cut it. Most folks seem to have either upgraded them to a "beefy" Meriah, or pulled them and put (2) 12" sucker style fans behind the radiator.
Parts........There are a plenty of Pantera vendors out there, and the motor is your Ford 351 Cleveland (if its still in the car). A caution though, when looking for any engine related parts at your local Autozone, Napa...etc,......just say its for a 1971 Boss351 Mustang. (trust me 50%+ have no clue what a Pantera is, and their DB's have no entries for it).
On your a/c question......I'm by far no expert, but believe that the US 71-74's all came with A/C, PowerWindows, Black interior seats, and either gray or black carpet.
What you may want to do is find a local owner that can check the car out with you, and also get a list of items or upgrades the current owner has done. Ask lots of questions, and post anything of concern on this site for an answer.
I'd throw this out there. For the $$ I've put into mine, and I call it mostly restoration and upgrades.......I have never thought about selling the car (and this is a first for me). I fully expected that for an early 70's car you will need to put in some restoration funds. The enjoyment from owning this car, driving it, and having the non-typical auto is amazing.
Bob