The Pre 89 Thunderbirds are just mustang underpinnings correct? So is it possible just to bolt in a shock that is designed for an 88 mustang?
I think Chuck is making an adapter to do it. Ask/PM him
Take the time to do a little looking around the site and you'll find all the info you need on this.....it's been covered ad nausium.
In short you can use Mustang struts on the front, but Mustang shocks are too short for the rear.