shims? I don't see why you would need shims. :dunno: as to the clips, I used a thinner bolt before (see photo below), but later removed it and have been running the stock clips without bolts for years with no problems . the only thing is that when up on a lift, it's possible for the upper leaf to pull out and then catch the very edge of the clip when the truck is put back on the ground. a quick whack with a hammer puts it back in place. only happened once so far.
the one thing you will need for sure is a new center bolt. I used a grade 8 allen head bolt from the hardware store. You should also replace the U-bolts, as thy stretch when installed and can weaken if re-stretched.