i think the 89+ has thicker leafs like 3" as where the earlier are 2 1/2. not sure on this though
6" usually refer to bolt holes center to center...
shackles only lift half the spring so if you have a 6" shackle and you put a 8" set on it would be a 1" difference.. unlike if you throw a 2" block in you would get 2" of lift...
lol... those shackles suck... but they work for me at the time being, and i ALWAYS carry my stockers, just in case lol
This actually depends on your shackle angle, which will change with shackle length.
If you need a custom length shackle, just go to the steel yard and get some 2inx3/8 starp. Cut it into 4 pieces, than clamp those 4 pieces together and gang dill all the holes all at once. This makes it much faster, and you know that they are all the same. If you wanna get real fancy, grind the corners round.
Remember that shackles are not a science. What works for me may not work for him or you or the next guy. I would say if you don't have the equipment to make your own, order the big ones from Marlin, and find a fat anti wrap leaf, cut it so its just a block and add it to your leaf pack.
PZ