You are right about the thread size for the front tang screw that is common on all Win models ( not reproductions). Also sometimes called #10 -36. I have fitted several Win tangs and the guns vary quite a bit as to screw fit . usually tight. so a tap to chase threads with Kroil added is a Plus.
The machining they did over 100 years ago is quite admirable when you think of the crude methods they had to make precision taps for instance and heat treat them just right. 
  Also the old tang sights were much more solid then . the new Marbles and Lyman wobbly sights are an embarressment to modern manufacture