I've mulled over doing something like this for a while, but put it off because of technical challenges that turned out to be not all that challenging.
The spump part is pretty run of the mill: slotted the striker and filled in the cutout on the valve stem.
The lever action part is made out of steel and a plastic that I think is HDPE. It pivots on a rod that I put through the grip frame just in front of the safety. The various parts are all held together by 6-32 screws.
The action itself is pretty smooth, but the ergonomics are pretty unpleasant. I'll probably have to wrap something soft around the front bar for the benefit of my fingers.
More random pictures of the build can be found here