My 1985 that I used to have had the same saggy problems in the rear. P.O. was a friend of mine and gave me for free (along with the truck which was free) a rear spring booster kit. I never put it on, but I still have it. Do helper kits like this work? Personally, I would just as soon replace the rear leafs with decent ones rather than limp around on rear leafs with the frown "forced" upside down.
As for the rust, I can deal with it. There are still a couple of junked 4Rnr's at my local salvage with panels that are in good shape, but either way, I would rather have rust all over the body panels than have engine/transmission problems. It's easy for me to do susp./steering work, body work, but I don't have the space, tools, or know-how to tear too deep into these trucks...yet.
I actually talked to the kid again last night, and he said he's never noticed that it's burned/used much oil, the P.O. before him was getting around 24 mpg, and since he put on the 33's, he's been getting 18-20. That sounds pretty good to me, as my '85 was getting 23-25 in primo shape. I'm just hoping that it shifts well, 4wd engages well, and it runs decent. The kid said he'll throw in the timing chain, gears, and gasket that he recently picked up but never installed. Would changing this stuff be a fairly reasonable task? The only other thing I've timed is my '76 honda 750, and you just line up a mark. Oh well. I'll let you all know tonight if I can finally get rid of the jeep I've been driving and move back to fun vehicle.
-Chris