I put a 4.3 in my Trooper from a 2.6 and I also used the 4l60 Trans that came with the 4.3. You need a np208 or np241 transfer case out of a pre 1988 truck or 1991 blazer/suburban. It is not super hard but I would not attempt it unless you have some skills.

I could do the swap for you but I'm in Oklahoma and I see logistics problems there:D.

From what I have researched, if you do a 3.4 swap, almost any auto mechanic that installs engines is capable of doing the swap. The reason I say that is because GM no longer makes the 2.8's and they sell a "direct replacement" 3.4 This constitutes a equal swap if a dealer will do such an install.

The 3.4 will give you much needed power but it doesn't come close to matching the torque of the 4.3. If you just need it for a DD then I'd go with the 3.4.