I have restored three of my old Eveready brushes. The originals were from left to right: 750, a 40N and 40R. The 40R was the best of them, but the were all pretty well used up. I think I bought the 750 in 1963, and the rest were newer.
The Knots were all TGN 22mm. The Left one is a Best, (a little too Soft). The Center is a Silvertip (a little skritchy but not too stiff) and the Right is a Finest, Extra Hair (Just about right but not quite stiff enough).
I used a Forstner bit and a Dremel to clean out the old knot. I dinged up the end of Silvertip (40N) and had to turn it down a little to clean it up, but it came out fine. They are all set in Epoxy and all have been used a dozen or so times. They all had Ambrose's "Get the Funk Out" treatment, which they needed to varying degrees. (the Best was really bad to start with) They are all set about 1/2" deep. If I were doing it over they would be deeper. My favorite brush is a Simpson Col X2L and that is what I aspire to in my bush making attempts.
I'm going to turn some cocabola (think rose wood) handles and try some more later this Winter.