I recently swapped from Sidewinder to Predator Tactical. It is not a perfect fit, since the Sidewinder cut is wider at the bottom. I solved this issue in a MacGyver manner by simply putting a couple of layers of duct tape in the bottom of the dovetail cut between the slide and racker...
It may sound silly, but it actually works wery well. I have shot about 2000 rnds with this setup, and the racker hasn't moved a bit. The set-screws will mash snugly into the tape and force it to stay put.
Also I am very happy with the Predator racker. The reason for me wanting away from the Sidewinder was that may hand had a tendency of slipping off the racker. This is not an issue with the Predator, as it has a very rough sawtooth grip pattern (which is why the left and right side predators are different) which also looks cool.
Here is a pic of the racker on the gun. Sorry about the cell-phone-bad-lighting quality, but it gives you an idea of the angle, and such...
Hope this was helpful.