Are the ring and pinion gears chipped/broken? You're going through an awful lot of extra work and expense to keep the same gear ratio. And there's a significant chance that the pinion depth won't be correct, sabotaging the installation.
When this was me--well over a year ago--
I crammed a Truetrac into a 14-bolt Full Float axle.
I have the parts (Differential, and side bearings, plus a shim kit) to do the same to my '77 Concours (Nova) which has a similar 8.5" axle to yours, but with 28-spline axle shafts instead of 30-spline like most of the GMT400 8.5" axles.
LEAVE THE PINION ALONE. Don't dick with it at all, if the seal is still holding grease.
Re-use the ring gear,
after verifying backlash. Put the old ring gear onto the new differential case, install the case with new side bearings (no pinion bearings or crush-sleeve needed.)
Get the side-bearing preload right, and dick with shims as required to achieve the SAME backlash as the gear set had previously. The gears are now running in exactly the same relative positions as with the original differential case--they should be exactly as quiet and durable.
Saves you the trouble of getting pinion depth correct, pinion bearing preload/crush sleeve torque correct, and therefore simplifies the differential case installation--IF (big IF) the original ring and pinion gears are in usable condition. You could send the ring 'n' pinion set back, along with the "master installation kit". You need two bearings (about $60) and a $20 shim kit.
For those of you limping along on damaged 8.5" differentials--open or Gov-Bomb--keep in mind that when it does explode, it's going to throw debris between the ring and pinion gear, locking them up and skidding the rear wheels. The vehicle will be essentially
uncontrollable, with the ass-end swinging left and right for no apparent reason.
Hopefully you will not kill people.
