He covers everything you need to do on his 5 lug conversion page to fit the SN95 brakes on a Fox. There are several step by step how to install pages also around the web.
To use the 97 brakes on a 90 you have to swap over the whole spindle assembly and switch to 5 lug wheels. People do it all the time, but it's not just as simple as bolting on new calipers and rotors.
you may have some rubbing issues with the 97 brakes since they sit out further then the sn95's. You will also need to swap to newer balljoints or use a .330 spacer. In my opinion it is worth it as I have done this myself and would do it again if I ever buy another stang. I used the sn95 setup though. I would go with the PBR brakes off a 99+ mustang too.