The ruffstuff kits are about as close to a "kit" as you'll get. Forget sticking with the weaker toyota diffs and use the widely availble GM dana 60/14 bolt from a 80s CUCV. The axles sets sell for $1,200, come stock with 4.56 gears, detroit locker rear, and are cheap and easy to rebuild before swapping in. Shave the bottom of the 14 bolt, spend a couple hundred on new bearings, seals, front lunchbox locker, and rear disc swap, front jeep coils, mount a saginaw box on the frame, custom lines from pump to the box, etc. All that stuff is fairly basic tech on pirate4x4 and other sites, but I think everyone here is stuck on staying 100%, but the main issue is there isn't really a toyota solution to the SAS.
http://www.ruffstuffspecialties.com/catalog/
http://www.ruffstuffspecialties.com/catalog/3LINK-COILB.html