Turns out a new gun will take more filing and working to get new parts in than an older version.
Case in point I'm installing a flat trigger and a steel mainspring housing in a AL frame 4in 1911 I'm making as a gift. It was a bit harder to get the parts in this time than it was on my 1911's.
Guess all that "break in" and "everyday wear" adds up.
And as always be patient and don't try to force things. Also a small metal file, calipers of some kind, and the original part are your friends.
Gunsmithing is in scare quotes because I'm just doing parts swaps.