TBI or TPI? 92's never came with 350s and 5 speeds. Sounds like its a truck TBI 350. Nothing wrong with that, plenty of power for a small truck like this.
Check the casting numbers on the tranny. I'm guessing its a t5 or the like but that generation F-body had 2 separate trannys, one for the v6 and one for the v8 (same bolt pattern) but the v6 had a super low 1st gear and a big leap between 2nd and 3rd (I believe).
Any GM front axle will work, a dana 44 is best but a 10 bolt will survive a while. As far as gearing check what you have stock, it should be ethier 4.37 or 4.63. The way you tell is by checking the fender tag on the passage side fender for a HG43 or HG46. You will need too regear the front axle too meet the needs of the rear unless you swap both out from the same donor.
The rear axle is plenty strong for just about any need a pathfinder owner should have. Unless you have massive tires and lots of jumping then I would look for a 6 lug 14 bolt. Now the 14 bolt is bullet proof but very heavy and fat.
Leaf springs, you can run after market ones or ones from the junk yard.