dd is win for clearance.
diffuser is fail for clearance.
one thing i always do with my exhausts is get metal spikes and put them hanging from the rear of the tailpipe. usually you can screw them into the little hole for the silencer. (you can see what i mean in the above pic).
the spikes i used are these ones. they're like a buck
that way the spikes drag on the ground, not your exhaust.