If you are using a Detroit type locker it will replace the stock ring gear carrier anyways. Usually once the spiders are welded it's almost impossible to get them out without damaging the carrier. Since you are also replacing the ring gear, pinion and all of the bearings, there is very little of the original rear end you are reusing other than the housing and axles.
If you reuse the stock shims without taking the proper measurements, chances are pretty good you will end up with a bad setup that will for sure make noise and could wear prematurely.
Rent or borrow the tools to allow you to set the pinion depth and preload correctly. Setting the ring gear backlash can be done with a Harbor Freight dial indicator and torque wrench.
You're spending enough on the parts that you are better off paying someone who has the tools and knowledge to set it up right if you don't have the tools. But if you have the tools and can follow the step by step instructions that come with the new gears, you can certainly do it.
Depending on how many miles the rear end has on it, you may also want to replace the bearings on the axles and the seals at the end of the axle tubes.
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