Glad I could help a little bit and Yes it's is a ordinary right hand thread on them.
It's quite common those are missing, as a fact I looked for one for a IWC 66 a while but ended up making one.
If you look a the sqare stem you will find a small hole in it, it's where you put a thin pin in to lock the finger piece into place.
Good job. That was smart using that compass(?) for a "special wrench". I can't remember what I used. It might have been a junky set of tweezers. I'll remember the compass-tool.
Bob Tascione has a nice animation of the workings of the stopworks. In it, you should be able to see the shape of the part you need. It's on youtube. Search his name and you'll find it. Good luck.
Hi All advise given is wise and should be noted, also consider lightening the inside of any desk/work place so as to give good reflection of light. My workbench is covered in white lino tile, a pale green as per the bergeon mats etc. as Marc says the roll top is probably the best option.