I must not be thinking about it correctly. Please tell me how I am not getting what you are suggesting.
I get it that any of the people you suggested could cut a feed neck, mill the body, cut a hole for the valve to dump into the bolt, drill for mounting screws for grip frame/beavertail/lock nut for ivg, drill a hole for the hammer lug, etc..
I looked at the extrusion on airsoldier. Two straight bored holes the length of the body. Slice a chunk off and there still isn't enough to get the ram and the three-ways mounted in the right spot on there. Slice a chunk off and there is nothing to pull the cocking rod back either.