8.75 or Ford 9”???

With a stick? Definitely the nine inch, and figure Lots of good parts in it. Locker at least, spool if race only, 35 spline axles (or more, if spool) new nodular or aluminum case, and a backbrace or fab housing. And lots of tire.
All the best parts available for an 8 3/4, it wont be as strong as a 9.
Edit: someone here will suggest that if you wanna keep it mopar, use a dana. When i am asked, A or B, i dont answer C!