I searched and prob just not looking right. The tag says:

WDM-BA 4BA
3.50 9 316A

Mainly just concerned with year and application. Thanks!

 

Never mind. Found it here:

Ford Rear Axle Assembly Identification - Page 01 - FORDification.com

 

That site is great, full of info.

 

while we are on the subject of Ford 9" rear ends can anyone tell me if it is possible to cheaply convert a 28 spline posi to a 31 spline? Is it change the spider splines and go or is it part of the locker?

 

Swaping from 28 to 31 spline in the differential is just a matter of changing the side gears. But to do it does require a mostly complete tear down of the diff unit and reset of the gears. That takes it out of the realm of cheap or easy, in my book. You'd have to want or need it really bad to go through all that, because the standard 28 spline stuff is plenty tough.

 

I have rebuilt several dozen rearends over the past 45 years. I just never payed attention to the side gears and was not sure if the posi took the same gears. No problem to set the backlash and contact area. It just takes the correct tools and a bit of patience.