I've got an armored 80 on 37's (all I have is RCV shafts, 4.88 gears, and t case gears, with factory locked axles). In order to run this setup you don't need to do a solid axle swap, upgrade steering, etc. To run a similar setup on a newer taco or 4runner you are looking at a lot of work.
I try and wheel my rig pretty hard (I was in Johnson Valley today and I intend to run Clawhammer and sledgehammer in a few weeks). In my opinion the 80 will make it through most trails, although it may not be pretty. Yes it's heavy, but what really holds it back is a lack of gearing options. Compared to a 4 door wrangler it's wheelbase isn't much different nor is its width. It's wide, but it fits through everything narrow I've seen.
Now, if you are into serious rock crawling, the kind where there is no trail just a stack of boulders, go with something that gives you super low gearing or build a buggy. If thats not your shtick, the fat lady (80 series) will work just fine. Stick a winch on the front and if it gets really bad use it. To me, nothing beats the room, build quality, or all purpose nature of the 80. If you want a 100% crawler and that's all you want to do, the 80 is probably not for you unless you bob it, swap the drive train, and put it on a diet. The problem with the 80 is no matter what you do short of a drive train swap you can't get around the low range gear problem that is needed to make a real rock crawler.
Bottom line, figure out the trails you want to run, how many people/cargo do you want to carry, and how much modification are you willing to make then work backwards to the ideal vehicle. You can run 35s on a stock 80 with a 2.5 inch lift and nothing else. What other truck let's you do that reliably and for dirt cheap?
