Axle Help!
 

Its finally time to rebuild the rear axle of of my 99 jimmy after 150,000 miles.
I'm in the process of buying all the parts but I'm having a hard time figuring out which axle I have. It could be a 7.5"rg, 7.625"rg or a 8.5"rg.

Does anyone know how to tell these axle apart without taking anything apart?

I've read that you can disconnect the drive shaft and remove the flange to count the pinion splines.

7.5 = 26 spline
7.625 = 28 spline
8.5 - 30 spline

I've also read on the Richmond gear website that the 7.5 came in 4cyl models the 7.625 came in 6cyl models and the 8.5 came in z71 models (I think its supposed to say zr2 not z71)

But then I read the the 7.5 and 7.625 covers are more square and the 8.5 cover is round. This confuses me because my rear axle cover is round but not a zr2 package.

Does anyone know of a easy way to identify the rear axle? or am I going to have to pull the drive shaft mounting flange? Heres some specs on the truck maybe someone will just know by the options.

1999 Jimmy
4.3L/4l60e
towing package
4wd
GU6 axle code (3.42 ratio)
sle