Listen to Fubar's post, that is great advice on how to change the leaf springs.
A couple things.
Get new u-bolts. U-bolts are meant to be a 1-time use only type of bolt, as they stretch when they are torqued down. Just because they look good doesn't matter.
I also have yet to find u-bolts in my local hardware stores. Yes you need specific ones, as you need the corresponding u-bolts for your axle tube diameter. I know RuffStuff sells very beefy u-bolts. As far as the length of the u-bolts, that doesn't matter as much, as you can always cut off the extra threaded part once you have installed the axle.
... I just installed new shackles on friday, well now Ive got to get new leaf springs b/c the shackle is bend down my leafs...
Right now I have 2" blocks and 2" leafs with add a leaf.
The shackles have nothing to do with you needing new leafs. I'm assuming you put in longer shackles? The reason why it looks like they are "bending down your leafs" is because the leaf spring now mounts farther away from the body, so you can see it more. The leaf has always been bending like that, you just probably couldn't see it before. Shackles don't wear out leaf springs, blocks do. (blocks are alright on heavy duty leaf springs, like the ones on trucks, but not on light duty leafs that the XJ uses). The leaf is mounting in the exact same place, so there is no added weight on the leaf, and nothing is "pushing it down."
Ya i know its the block. the blocks are pushing up on the leafs, and the shackles are pushing down. the blocks arnt letting the shackle do what they are designed for.
Whether the blocks are there or not, the leaf springs experience the same force vectors at rest. The weight of the vehicle is on the axle, so you will have the axle or block "pushing up" on the leaf in the middle, and you will have the weight also "pushing down" on the leaf where it mounts in the front, and where it mounts to the shackle.
As far as the blocks not letting the shackle do what they are designed to do, that makes no sense. A shackle, lift or not, is designed to compensate for the change in the length of the arc a leaf spring when it compresses or extends. This is why you can not have two solid mounting points with a leaf, as they would wear out incredibly fast, and fail. A block does not interfere with this, or anything the shackle does.
When you put your new leafs in, take the blocks out, otherwise the same thing will eventually happen to those leafs. The block puts extra leverage on the leaf, and causes them to wrap and twist. This quickly will wear the leaf out, and sometimes cause it to break. The farther away the axle, (bigger block) the more torque on the leafspring.