I'd be interested in the scope/scope rings, cocking lever, the cast rubber grips (you should probably make these with a bit of bleed, since not all 3D printers are created equal) and possibly the LED stuff (any chance of adding sound, too?).
I'd also be interested in the 'End Cap 2' (d-ring) part, but I think this is an area where we can improve on the original model and make it more screen accurate - the original mounts to the OUTSIDE of the end cap, so the flange is not necessary, you could just thread the inside and you'd just need a screw + washer to mount it.