Any type of coil over setup is going to cost you an arm and a leg if not a first born. I talked to quite a few about it and decided to pass. There are other ways of going such as modified A-arms with bearings instead of rubber sleeves. And there are custom made A-arms and custom made lower control arms. Check out this site:

http://forums.vintage-mustang.com/index.php?

Go to the forum. You'll find all sorts of suspension guys that make custom stuff. Lots of guys race vintage Stangs It's the best vintage Mustang forum out there.