Yukon, USGear, and GM all make gears for both axles. The front may be tough to find but, the 8.6 rear is very common. I have a set of used 4.56 GM gears (31,000 miles) for the rear in perfect condition...$100USD. They came out of my H3 when I swapped to 5.13s. Everything I've taken out of front diffs has been broken (big surprise).
Swapping the gears is not too big of a deal, especially if you keep the same carriers and bearings. You'll need:
-a bearing plate
-a shop press
-dial-calipers
-dial-indicator (with a magnetic base)
-a torque wrench (30-150 ft-lbs range)
-an inch-pound torque wrench (with a dial on it)
-a large pipe wrench (to hold the yoke while you crush the new sleeve)
-a few basic hand tools
-marking compound
-loc-tite
If you can get your pinion bearings off in one piece...you can simply press them onto the new pinion gear with the same shim-stack, assemble it, check the lash and pattern. Most of the time you'll be spot on but, sometimes you need to add or subtract a pinion shim to get the correct wear pattern on the teeth. You can leave the carrier bearings alone...just keep the shims & races in the correct order. Again, you may have to make a slight shim adjustment to get the lash correct. If you want to change bearings, you may have to buy a special tool to remove & install the pinion races into the casting. A case spreader is not needed. Set-up bearings are nice but not necessary. TIP: Check the butt-end of the pinion gears for a hand-written (or etched) number. This is the pinion depth dimension, and you can compare the number on the existing pinion against the number on the new pinion...and add/remove shims to keep the same depth. This works great and saves you a bunch of measuring and guesswork when setting the pinion depth.
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