I have a 99XL 4.6 manual ext cab short box. I want to make it posi! Will a 8.8 ford 31 spline posi work for my stock rear end? If not, what part would I need in order to make so.Thanx

 

Yes; however, the stock FOMOCO is not a posi. It is only a L/S.

There are many great options for the 8.8", such as Auburn HD, Eaton Posi, and Auburn Pro series. All decent for daily driven vehicles.

 

Dont mean to hijack your thread !
But will this equipment work with stock axles and if so where can you get the set up ?

 

Yes, You can take a stock "open" carrier and replace it with a Auburn, Eaton, TracTech, or whatever. Just be sure to add friction modifier if you are installing a unit that has clutches.

You would also probably want to replace the differential side bearing cups and cones when having the swap done. As far as having this done: you might try posting on regional boards of the F150 site for a reccomendation of a good gear shiop in you're area.