I think they came out of the rear for a reason; to prevent exhaust getting blown back over you in traffic, and to make it quieter. Bear in mind it's your passenger who will be affected most.
I've also looked at the side exhaust as mine had that set up in period. Judging by the exit point of side exhausts and the length of my current rear-exhaust, I think it requires a shorter overall box. I also believe they used slightly larger diameter pipes, but perhaps someone with one can comment.
If you find a source for parts or correct dimensions please share.