According to Sheldon Browns site, the bottom bracket is probably 1 3/8" X 26 tpi with a 71 mm shell width. Nothing at all modern will fit it- everything else is 24 tpi. So unless you can find a similar vintage bottom bracket, or just like to look at vintage frames, I don't think it's worth it. But I have seen Sturmey Archer 3-speed hubs for sale at very reasonable prices - you'd want to check the frame dropout spacing to be sure a new one would work.