[dsraven]

on the shackles, check to see that they are square to each other. use a flat piece of wood or steel and start by placing it on the one side bar so it lays down from one end to the other, then slide it across to meet the other side, they should be parallel to each other. with that done and the center bolt tight, get a dimension between the flat bars and do like mr48 says, cut a length of stout tubing, like DOM tubing, that the bolt will slip through and cut it to that dimension. then remove the bolt and install the tubing between the side bars as you assemble it all with the bolt running through the tubing. it will end up looking like the top pic of the shackle in post 5 except not welded to the side bars and it will have the bolt running through the tubing. a mod to that would be tubing cut slightly shorter with some larger flat washers placed at each end. these can be used like shims and then tack welded in place when done. a larger washer than the tubing may help stability because it makes the effective size of the tubing larger which affects a larger area on the flat bar. you could also make an H shaped part for the center if you think it may help, just ensure it will clear the spring on one end and the mount on the other end when the suspension moves through a full travel swing.