Can someone confirm if this will work:

I have a 91 RS manual trans with a 3.08 open with drum brakes. I want to upgrade to a 3.42 posi. I've looked around for junkyard 3rd gen axles with 3.42 posi, but can't find any. 4th gen axles with 3.42 posi are plentiful, but the axle width is about 4" wider than a 3rd gen, so that would screw up wheel position. My plan is to buy a boneyard 1995 camaro axle with a 3.42 posi and swap the differential parts (pinion, ring, carrier, posi differential) into my stock axle. I believe my axle shafts are 28 tooth spline, so they should fit with the 1995. I'm not 100% sure, but I think the carrier in the 1995 is the same as the stock carrier in my 1991, so that shouldn't be a problem either. I'll need to buy an installation kit to make the swap and beg some help from friends who are experienced with rear end setup.

This seems like a cheaper option than buying a posi differential, then buying the 3.42 gears and pinion.

Any better suggestions on the best way to switch from the 1991 3.08 open to a 3.42 posi without spending an arm and leg??

 

99% of all people who go with a 3.42 gear do it in the mannor you described. The only point of swapping the whole rear would be for the disk brakes (LS1 car).