1/2 ton 4x4 vs 2wd rear-end

[kevinr1970]

The rear-end in my '86 1/2 ton 4x4 (6-lug) has an Eaton posi and Yukon 3.73 gears and around 10k miles on it.
I am wanting to put this in my '87 2wd 1/2 ton (5-lug).

1) Is this as easy as just awapping the axles; 6-lug for 5-lug?
I believe that the spring perches and everything else of consequece are identical for 2wd or 4x4.
If I am incorrect about this, please let me know ASAP!!!


In the event that this swap is not that easy...

2) The '87 was previously a 3/4 ton (8-lug) and according to the SPID sheet in the glove box had 4.10 gears.
With a T400 I could drive comfortably on the freeway at about 65mph, any faster and it started to wind up a bit (I do not have a tach so I don't know exactly).
The 1/2 ton rear in it now came from an '87 1/2 ton swb that had a 4.3 v6 and a 4-speed manual (with the compound low). No posi.
I have only driven the truck on a highway with a 45mph speed limit but it seemed to be rev'ing pretty good at that speed, so much so that I was convinced that it was still in second gear but that was not the case.
The truck (crewcab) jumps off the line from stops and as nice as that feels, the max comfortable driving speed on the freeway of about 55 is not going to work!
Any idea what rear gears the truck with he 4.3 and manual would have came with; it was a Forrest Service truck if that makes a difference?

PS; 8-lug were 235/85(or 245/75?)-16 and the tires now are 275/60-15.