The clunk may be just because they are cheap coilovers correct?
Nick,
I am going to go ahead and send you some replacement rear upper strut mounts. I have heard of this once before and I believe that is probably your issue. Once you get the new ones please put the old ones in the box and ship them back to us. Let me know if this solves the clunking problem.
Was your car in a front end wreck by any chance?