Why those trucks can take so much abuse has a LOT to do with not being over powered. You start dropping a big motor in it you are going to start braking parts.
The easy swap is the 22RE with a W58 (or is it the 56?) behind it and the gear drive case. It will fall into the truck. The FI wiring will be very minimal to change out. You best bet would be find a crashed 4 runner and swap the harness over. The only issue will be that the VSS is in the cluster. You can get a drive through VSS that will gee the pulse you need for the ECM but retain the stock speedo.
The New 4cyl the exhaust is on the opposite side and gives a bunch of routing issues.
That said go look on Marlins site and Marlins son Mike (Bigmike on the forum) did a REALLY nice swap on his 80.
http://board.marlincrawler.com/index.php?topic=4401.0
WOW is that clean!
I had just got my Drivers license when those came out and I was crawling all over the one at the local dealer.
Expedition travel does not require big lift, huge tires. Most of the builds you will see here are a middle of the road. Better then stock off road but respectable street manners. Its not rock crawling. Its back country travel and camping.
As rare as that is becoming I would do a mild build being mindful of body mods. you might be able to run a 33 10.5 on stock offset and size rims without having to cut on the body. 33's with 4.88 is a well rounded gear. A 65mph your speedo will run about 2mph fast if it was a 4:10 geared truck to begin with. I can get 25mpg out of my 22E, 33 inch tire 4.88 gear 4Runner on the hwy. The key was the right gears and trying to keep the tire and wheel combo light (go with a quality alloy wheel the 33x12.5 on Alloy wheels on my 4Runner only weight 6lb more per wheel then the factory Steel with 235 75 15's it had when I bought it) Rotational mass is the enemy of axle shafts, braking power and MPG.
I'd consider a E locker swap in the back and a lunch box for the front if you can't afford the second E-Locker. You can still run 70 mph on the hwy being in the sweet spot of the 4cyl motors (they like to cruise between 2800 and 3200). Steep hills will still get you dropping into 4th but not so bad.
Suspension on a budget I'd run a mild lift like a 4 inch long travel springs and cross over steering to fix the bump steer the straight axles are prone. Some axle wrap control on the rear and Bilstein shocks. Thats going to be best bang for the buck and get some of the buck board ride out of it. Money no object I would 3 link the front and 4 link the rear with the Trail gear system and relo the tank. Only issue is that system is set up for the big tire rock crawl crowd. 4 inch lift is more then enough and getting the rear coil overs in will be tricky with out hacking the bed.