Ok I figured some stuff out. Want to post it in case it helps anyone. Yeah definitely want to keep the 4.6 gears.

I have access to a 1990 v6 auto as well. I'm told those have 9" rears and 4.625 which matches my 4cyl gearing. The Montero Sport axle is 9" and will give me a bolt in option since it's leaf sprung, and I can swap in the carrier from the 90 v6 Montero. I'm told that the 4cyl has an 8" differential so I can't bolt in mine.

I'm sure because of the length, and because my Montero is SWB I will have to use my driveshaft but I might have to swap that rear joint out or maybe drill the pinion flange to make mine work.

Can anyone confirm my findings? I'm grabbing this stuff this weekend.

Available gear ratios
http://www.starquestclub.com/forum/index.php?showtopic=73459

Thanks