when i do suspensions, if i use poly bushings, i only use them on the frame side to eliminate noise coming through the cycling of the suspension.
also it takes some of the rigidity out of the suspension. a little give is ok.
going down the highway though gets annoying without poly businges.
thats why i was wondering why they were chosen for the axle side.
but if you made the mounts uniform on axle and frame, then swapping them around would be a breeze