There are 2 sets of bearings in the rear diff, the pinion bearings and the carrier bearings. The carrier bearings get pressed onto the carrier, and the pinion bearings get pressed onto the pinion. If you are changing either the carrier, or the pinion, then in order to re-use the bearings they would have to be pressed off your current part and pressed onto the replacement part. If you are keeping your current open differential and only swapping gears, and if the current diff does not make any noise or have any issues, then the carrier bearings can stay, just make sure you keep the right race with the right side. What I usually do is as soon as I take it apart I use a zip tie to hold the race and the shim onto the carrier on the side that they are used for, that way you can't knock them off the table or something stupid like that and screw them up. As far as the pinion bearings are concerned, the only way to re-use them would be to press your old bearing off your old pinion gear and onto your new one. At that point, considering how easy it would be to damage the bearing in the process and how cheap a new bearing is, I would just replace it. Also, remember once you get your old pinion bearing off, there will be a shim under there that you need to transfer over to the replacement pinion gear. That sets pinion depth, and it is case specific, so whatever thickness that shim is, no matter what gear ratio you put into that housing, that is the shim that you will need. If you lose it, it is possible to determine what thickness you need, but it requires special tools and a lot of time, so do yourself a favor and don't take the bearing off the 3.27 pinion until you have the 3.73 pinion and the new bearing in front of you, and then do it all at once, and remember to remove the old shim from the 3.73 pinion first if it is a used gearset.
I read your notes a few more times and reviewed the following DIYs and I think I understand what needs to be done.
If I understand you correctly,
1) it sounds like I don't need to do the shimming if I'm going to re-use the carrier AND the pinion shims. I will also re-use the carrier bearings.
2) For my application, I only need to replace the pinion bearing that's attached to pinion gear itself or ???
Planned Shopping List
1) Basic 8.8" install kit
Looking at the deltra between this RATECH kit and the basic MOTIVE F8.8IK kit, it appears to be carrier shims (not needed) and the pinion nut.
What are the chances that I'll chew up the pinion nut?
2) Pinion Bearings.
Q: Which one of these two cup+cone sets is the one actually attached to the pinion gear?
According to http://www.corral.net/tech/drivetrain/gears.html
, I think it's the M802048 & M802011 aka "Rear Inner pinion bearing cup & cone" according to Rockauto.com. Please confirm.
Rear Inner diff pinion bearing cone part number M802048 $10.42
Rear Inner diff pinion bearing cup part number M802011 $5.10
Rear Outer diff pinion bearing cone part number M88048 $7.30
Rear Outer diff pinion bearing cup part number M88010 $3.71
Q: Just to clarify, should replace BOTH pinion bearings or just the inner one? The outer pinion bearing is relatively cheap and doesn't require any special tools (like a hydraulic press.) It's one more thing to screw up though so if I don't have to replace it by your recommendation, I won't.
Q: Lastly, since I'm planning to use used gears but a new pinion bearing(s), do I need to break in the differential?
Thanks again for all the replies. I've really learned a lot today.