I'm using a Savage X spur (the ones with slipper plates on both sides) together with the sliper discs from the RRP slipper kit which i filed completely flat. Im using another stock slpper spring as the bushing.
Works pretty good and looks like this :)
The usual savage spurs work too, but you first have to put a stock slipper pad (or a smilar shim) before the RRP Pad (and then the spur) to make it work. But sadly the only option of slip adjustment with this method is "air tight"...