from my scaling - the round disk that goes under the arch is about the diameter of a standard Dritz™ metal snap. But a bit taller. I just made one from a snap - and bulked up the height of it. It's about 1/4" tall. It will be cast in black resin - like the rest of the handle 
Good plan to just scale it to Kim... since there was not a lot of reference points or pix to go off of - especially back when you made yours.
Yup - my trigger will work. I think the screw on the side of the real one was there for that purpose... at least it will be for mine (as you can see by the elongated hole in my trigger). i will put a spring on the back of the trigger too... 
how did you create the larger base - that the barrel rests on¿
