I'm not a guru but AFAIK there are two different front diffs for ttb. The d-28 and the d-35. the d-28 is in all rbv's from '83 thru '89 and beyond in certain vehicles with motors NOT 4.0l. The d-35 is in rbv's [all the 4.0l have them] from '90 on until ttb stopped being installed. There is a hybrid in the early '90's that uses a d-28 guts in a d-35 housing.
There is a tech section -"info technical" at the top of the page that should have more specific answers and there is also the TRS Magazine that can be helpful. Also use the search function, it seems the "google custom search" at the top right of the page returns better results.
Good luck,
Richard