I finally got some parts in. I hunted for a smooth-flat main spring housing with a magwell to only find one, Smith and Alexander. I talked to a nice lady on Monday afternoon, and Thursday it was at the house. It showed up the same day my Ed Brown memory grip safety did.
Oh joy! ... no so fast hot rod.
The pin hole for the safety is drilled at an angle, and it causes the grip safety to cock itself against the frame. The S&A magwell-MSH isn't flush with the frame like I thought it would be. As a matter of fact it's not even symmetric side to side.
I called the nice lady at S&A, and she confirmed what I was thinking. The part was casted with extra meat to it so folks can checker it, dimple it, etc. Not good for me as I only want to polish it. I'd have to take 1/8" or so of material off the back of the MSH. I'm not sure I want to do this to a $89 piece without a mill. So I'm debating whether to send it back and keep hunting. I noticed that Fusion is coming out with a 2-piece flat-smooth MSH-magwell. I haven't confirmed yet if it'll be flush with the frame. I like the 1-piece aspect of the S&A, but I may have to go with the 2-piece. My Spingfield has a 2-piece magwell-MSH setup, and it's pretty solid so it may not be a major issue. I also like the fact that the magwell goes all the way back to under the MSH. The 2-piece design has the magwell stop short.
As for the safety pin holes. I think I'm going to have to send the frame back. There is no way I can make this work without a loose pin or a really loose grip safety. I'm going to need a new frame, or they'll have to weld it up and remachine it. I'm pretty disappointed as the rest of the frame is just great. Recall, this is one that was custom cut to match my commander slide, so I don't know what's going to happen. I can only hope for the best.
Below you can see the problem with the holes and how it causes the grip safety to be cocked (the is the best I can photograph in the light I have here, but it's a pretty accurate representation of how the grip safety sits on the frame with the pin just starting to go through the right side hole. The pin won't go through at all right now with the grip safety installed (ETA: I'm using the hammer pin to test fit the grip safety. The hammer pin slides through the safety holes effortlessly without the grip safety and it just about falls out on it's own if let it). The grip safety and frame actually fit nicely together without the pin. I'll need to file some edges on the grip safety and smooth the frame at the transitions, but the problem isn't the grip safety fitment.
(ETA: When measured from the TS hole to the MSH pin hole on each side, the left side measures 3.246" and the right side 3.257". These are not pin bore center to pin bore center, but bore edge to bore edge. The second set of numbers agree with the first set. My measurement uncertainty is +/- 0.0005. )
(the arrow shows less meat on the left side under the hole, and the 0.115" is between the hole and the frame just above the hole)
(the arrow shows more meat on the right side side under the hole, and the 0.104" is between the hole and the frame just above the hole)
One other thing, the firing pin hole is too small! I think it was drilled for a 9mm firing pin as my 0.0895" Ed Brown Hardcore pin won't go all the way in.
I was so looking forward to making some progress this weekend.