Every major city I have lived in, had a driveline shop that specialized in transmissions and rear ends. If you live near SW Iowa, I know a good shop that can probably pull a gear change off for you, the shop in mind is in my yard.
If you are going to do it in the chassis, its best to do it on a hoist or over a pit. The last thing you want to do when setting up a diff, is to get tired and impatient rolling around on a creeper. I have done it on jackstands, but would rather not to that again. It is much nicer doing them over a pit or on a hoist, or if those are available, pull the rear diff out and put it on stands in the garage to work on.
Michael
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