Here are my lessons from running 3 different RUF packs.
Lesson #1: Everyone builds them with too soft of a spring rate, making the spring bottom out and bend the axle housing. With 5 leafs the rate was 118in/lbs... with 6 it was 141in/lbs. The correct spring rate for these trucks is ~220 in/lbs.
Lesson #2: Flex + Leaking power steering eats bushings. I would eat a front bushing every couple months until I installed Prothane bushings. I still run prothanes to this day.
My first attempt were made from a 84 rear pack, and an 83 rear pack. My top leaf was an antiwrap leaf (its only supposed to be on the front half of the spring...) made from the main leaf of an 84 rear pack. I honestly think this leaf was worthless. Main leaf was the main leaf from a 83 rear pack, second leaf was the mil. wrap off the 83 pack, 3rd leaf is the stock 83 3rd leaf, 4th leaf is the military wrap leaf off the 84 cut down 3.5" shorter than the 3rd leaf on each side, the 5th leaf is the 3rd leaf off the 84 pack cut down so its 3.5" shorter on each side than the 4th leaf.
After lots of messing with the springs (upped the springs to be a 6-leaf pack, with more tapered leafs), I finally gave up and bought Old Man Emu CS009r rear springs. Night and day difference. This was mostly because they are 47" long, giving a better shackle angle.
If I made another pack again today I would do:
∙ 9-10 Leafs (217-235 in/lbs)
∙ 79-83 Main & 2nd Leaf
∙ Taper the rest of the leafs to match
∙ Run prothane bushings
∙ Consider moving the front hanger forward 1" to get a 35* shackle angle
Useful Resources:
Leaf Spring Rate Calculator:
http://www.jalopyjournal.com/forum/showthread.php?t=202296
RUF FAQ:
http://www.pirate4x4.com/forum/toyota-truck-4runner/265669-rear-up-front-faq.html
Roger Brown Suspension Page:
http://4crawler.com/4x4/4R_suspension-III.shtml