I've been doing alot of research myself on a similiar subject and I believe I can answer your question correctly. Look on Ebay for a factory radio out of 89-98 mustang without the Mach 460 system and it should just plug in. The radio's don't change just the harness capabilities.
So the plugs are the same all the way up to 98? I have been looking on Ebay but most of the cd units are bigger than my stock unit, and I can't tell from the pictures if the plugs are the same. I wonder if cd was an optionon 93 mustangs. If so it should fit an 89.