(actually done hours ago), and it works. I do think it needs a little polishing; that I'll do later(more information to be added later). At this point I'm falling-over tired, and worried about friends(short version: daughter, who's been pushing her luck for a long time, really screwed the pooch. More complicated than that, but that'll do).
Update: the thumb safety on a 1911, when pushed up to the 'on' position, rotates a piece into place against the legs on the bottom of the sear, locking the sear nose into the full-cock notches(also called hammer hooks) on the hammer. A very positive safety.
Considering the number of people making parts for 1911-style pistols, it's common to have to do a bit of fitting on one of these. Rather than duplicate a couple of very good pieces I'll refer you to the M1911 Forum site: a very nice piece using a cutaway to show exactly how the thumb and grip safeties work, and fitting the thumb safety here.
I used a stone instead of a file(takes a lot longer to mess something up that way, so more chance to spot it if you're messing up) so it took me longer than it should; in any case, works perfectly.
I think I shall get into the shower*, clean up, read a bit and then crash. Hopefully missing the floor in the process.
*Still not actually a shower; still haven't been able to break the threads loose. A pain, but not a horrible one; I still have clean water and a drain.