OK, I've been thinking about this, and I one seen that the 87-88's are the same length as the 94-04 Mustang A-arms, but the SN-95 ball-joints are different and will not work with Fox spindles. Could you use the SN-95 a-arms, and do the SN-95 5 Lug Conversion with that?
What would that do to your suspension? What would be the benefits of using the SN-95 A-arms?
I've been thinking about this, and want to do a 5 Lug conversion to my 87 Cougar.
This has been discussed almost ad nausium elsewhere on the site.
You can use the SN-95 spindles on the Fox ball joints with a spacer under the nut, or swap SN-95 ball joints into your Fox arms. The only "benefit" of the SN-95 arms would be newer bushings as the balljoints are swappable, so no gain there.
If you are gonna do the work why not just get a busshing kit and replace them all. Also coolcats has a good 5 lug swap on it. Think it uses the lincoln fronts but mustang spindle. With your bird A-arm.
If your stock bushings are shot and you want to replace them anyway, then getting the Motorsport SN95 A-arm kit would probably be a good move, but only if you plan to use SN95 brakes. Otherwise you'd be backtracking (Fox ball joints, Fox 5-lug swap, etc.).
The SN95 brakes have the newer sealed hub-style system that makes doing brake work much easier. You also have the benefit of using newer-style parts, which means parts availability in the future is very good. Weight-wise, I don't think SN95 parts are any lighter but they don't feel any heavier to me. After having done both types of swaps (Fox, SN95) on the same car, I have to give the thumbs up to the SN95 system. It's a cleaner install.
For a stock application (i.e. not road racing), use 1994-95 Mustang spindles. If you're going to lower the car and/or dial in agressive caster/camber using c/c plates, then 1996-2004 spindles are better. You would also need a pair of Steeda X2 ball joints and a bump steer kit.