This depends on how deep your wallet is. If you have the cash, you can't beat CCW Classics:
Complete Custom Wheel - Classic /// Wheel Profiles
Those are a true 3 piece racing wheel though, but the up side is you can get them in black or silver (even gold i think) and just about any size and back spacing/offset you can think of. They're easily close to 2K for a set of 17x9s though.
As for the ARE's, they're out there but you have to find'em. I literally searched for 4 years for the set i have, and they're perfect except for 1 ding in one of them that can be fixed. I also have another set of 15s for my Merkur. The 15s are easier to find than 16s, but IMO the 15s don't quite look right on a Mustang.
A couple things to think about when looking....these wheels SUCK big time to refinish. Stripping them is an all out nightmare no matter what chemical stripper you use (i've tried everything available to the public). You can expect to pay a good $400 for a decent set of 16s.
Alternatives are the Lincoln Mark VII rims and Crown Vic rims, which are both 5 lug. I'm pretty sure they both came in 16''. I've heard the Crowns have a funny offset or back spacing that may not work on a Mustang, and nobody i know has tried to mount them yet.
Lastly, center caps are scarce as well. You can go on ebay and find knock offs, which aren't all bad, but the real ARE or Riken caps are tough to find since they usually stay with the rims, but they're out there too.
