I run all 8 leaves on my FJ55 rear packs in the back of my FJ40...plenty soft, no top, no rear passengers. I run all 8 factory leaves plus one additional leaf in front, even with the lighter V8 motor.
IMO, it will limit up-travel a bit, but might be needed to keep some load carrying. Could go...
get the springs and hangers, go from there.
I'm not a fan of folding/scissors shackles....they do add articulation and are great for some areas, especially if you do a lot of "flattish" boulder crawling. They are marginal on steep uphills and IMO dangerous on steep downhills (tend to unload)...
honestly, I don't think there are enuf issues on the grade5 versus grade8 discussion to care....the general rule is, grade 5 for shear, grade 8 for tension. You'll find arguements for and against that all over....
If these were airplanes, I'd worry. They aren't, mine contains a mismash of...
hhhhmmm....let's see if I cover all the answers or not....
-Yes, it can be done in a weekend.
-40/60 u-bolts are the same...might need slightly longer since I'm guessing the 60 packs are slightly thicker
-55 rear packs have a slightly smaller spring eye and do work in stock 40 solid hangers...
it will move your axle back, will require driveshaft lengthening, will require work to relocate the shackle hanger, will require some "adjusting" of the solid mount to squeeze in the larger diameter spring eye of the 60 packs, will require custom shock mounts, and more.
That said, it's a great...