When you say shift fork you are talking about the clutch fork correct?Only time I've seen what I think your describing is a broken shift fork and being stuck in that gear.... If rocking it got the shifter to move I would let the clutch out slowly make sure the shift lever matches the gear your in or put the shifter in neutral and see if really is.. When I had it happen on a t5 it broke in 3rd and did not want to come out of gear with the handle.... Managed to manhandle the shifter but the trans was still stuck in 3rd until I pulled it apart to fix it shift fork was in 3pcs and fubar.
I am thinking it could be master or slave cylinder based on what i am reading for symptoms. Here is a dumb question, where is clutch reservoir typically for these older foxbody models? I want to check the fluid level. Please do not be afraid to ridicule me if I am being dumb.
Next question, what is difficulty level of replacing either?