early spf' rear ends were from 94-97 Thunderbirds, but believe some mods were made by spf . some even had the steel diff while some had an alum diff ( my 156 is steel ). bushings should be available from your spf dealer. I am not sure which dealers have a parts website . this one is from Hillbank - parts supplier for spf - and they have a website you can navigate thru :
http://www.hillbankmotorsports.com/
pick superformance and make your surfing selections.
they also have a pick for rear suspension that is for 'old syle rear axles'.
call your local dealer first would be my choice, should not be an issue. not sure if each dealer has a similar website or not. seems odd that hillbank would have one under their dealership name and not under their spf corporate name , as they are both in this case- dealer and importer ? hmm.
now, is the same part available thru ford ? I dont know the answer to that one, i know the spf cv boots differ from the ford boots, at least they did for my car.
there was a rear suspension bushing 'recall' of sorts on early cars some years ago....don't recall the details, but ask your dealer what impact that has on what you need, ie, do thier corporate records show it was done to your car. different serial numbers needed different fixes, they should sort that out for you.
otherwise these older cars keep taking a licking and keep on ticking as timex used to say yrs ago . bill, motown, spf 156