I left the retaining clamps, but didn't put in a bolt. it's only been an issue when the truck was up on a lift and the leafs max out (and even then it's only happened once). a quick whack with a hammer put everything back into alignment.
don't know what the center bolt is, but I was able to get one at the hardware store that was grade 8 and had a round head on it (the ones that take the allen wrench).