Very nice. Coincidentally, I have also recently received a IA (Ingvar Alm, the late designer and famous airgun collector) mount from Mac1, and the adjustable piston.
Tried to finish adjusting the piston this morning before work, but there's a bit more tinkering to come.
It will be interesting to read your results.
The current length of the Mac1 piston is a tad more than the original one, but it isn't long enough: correct me if I'm wrong, but I think the pump cup should make contact with the valve on closing the pump arm. Just a bit? I can't feel that atm.