I have a steel mainspring housing on mine, like you said. It came off a vintage blued 1911, but was Parkerized before I bought it out of an orphaned parts bin at a show.
The Thumb Safety is a modified smoothed aftermarket version that sits flush with the frame.
I went with all flat mainspring housings and ambi safeties because I'm left handed. The Ed Brown safeties are a little better than the others because they recognize the need for a larger right side safety for us "other handed" people. I don't mind the Glocks for the safety issue. I don't like them because life's too short to shoot ugly guns.
Bone grips on my son's[now my] ported Champion.