How hard would it be (on the screwless frame halves you are talking about) to just clamp them together with light pressure, drill and tap a few screw holes right through them both, and put screws in there as temporaries while you are milling? Then take the screws out when you are done. Unless the mechanism is going to be bothered by a few extra holes in there, I can't see what harm this could do. In fact, you could fill up the holes with tungsten rod when you are done and gain a wee bit of extra weight.