I don't run one, but this is what I've read
a truss on the bottom works best for jumping and crap like that, but sucks for trail riding because it hangs up on obsticles
I don't see any problem running them on top of your axle, except maybe hitting your body during compression
some guys integrate their link brackets into their truss, if you want to build a custom suspension
if your gonna weld one on, some people say to be careful because the heat can warp your axle housing
also, keep your ground close so you don't weld your bearings, etc.