I'm not talking swapping whole rear ends, just the posi- units. Can I take my 3.42 posi with 28-spline and swap them into a 4th gen rear and remove the 4.10's? The 4.10's is obviously overkill. Just wondering if it's possible.

Reason I ask is my friend has a 4th gen rear with 4.10's he'd sell to me for $200, the same price as an axle. The rear I just put in has a bad axle, a custom made one was bought and shipped out but it was the wrong spline count (needs to be 28, not 26) and no one has an axle in good condition. Just wondering.

 

yes, you can swap posi units and gears, but you still need to get an axle for your rear.
i've got 4.10's in my 3rd gen 5 speed and they are awesome.

 

I can't use the 4th gen axles? I was just going to put in the complete 4th gen rear, but swap out the 4.10's for my 3.42 posi. See what I'm saying? I know it's confusing. Hell I am pretty damn confused myself as what to do.

 

Ok, I see what you are saying. yes, that will be fine.
It sounded like you wanted to get the posi and gears from the 4th gen axle and put it into your 3rd gen rear.