1971 GMC C2500 rear end questions

[Baime]

A description of my truck:
- 1971, GMC, C2500, leaf springs, stock 10 bolt rear end with 4:11 gears, stock T350 3 speed transmission, 8 hole wheel patterns.

Based on some older posts on this topic, it sounds like there are several brands/manufacturers of stock rear ends on GMC C2500s. I have no idea which one I have, but it has a 10 bolt pattern with leaf springs.

What I'm trying to accomplish:
- I would like to change the rear end differential gears in my truck to improve highway driving. A fairly knowledgeable friend recommended that I change the rear end gearing to 3:42, or change the trany over to a T400R4.
- If I'm changing out the differential, I was hoping to change over to a posi-traction differential in the process.

My friend recommended a guy he knows who changes out differentials as a side business. What this guy said:
- My old GMC rear end is an "odd ball" rear end, and there are very few replacement differentials with different gearing, and there are no posi-traction differentials available for that rear end. He said I would have to change out the rear end with a newer version to make these changes, and cutting and welding would be required. The newer rear end would not just bolt in.

My questions:
1) Is a new 3:42 differential available for my existing stock rear end?
2) Is a 3:42 differential with posi-traction available for my existing stock rear end?
(I'm confirming if that guy knows what he is talking about, that these are unavailable. I thought I found one an an Eaton page, but I'm not sure.)
3) If I decide to change out the whole rear end assembly, is there a preferred/recommended replacement rear end to use for my truck? Will it require cutting and welding?


Thanks for you comments.

JP