Removing slip-on sidepipes can be a real challenge, especially if you are the only one performing the task. I removed the springs from the sidepipes and collectors and found the sidepipes were quite difficult to budge, let alone remove (poor design, flanged connections are the way to go).
So, after some thought, I hooked one end of a come-along to the sidepipe at the 90 bend (covered the sidepipe with towels so not to scratch) and the other end to my garage wall and proceeded to tighten the come-along slowly while I wiggled the sidepipe. Worked fine on both sides. No rubber mallet, no damage to the sidepipe outlet through the fender, no sweat and better yet no cursing!
Phil from Phoenix