I just took measurements off my 1927 22-YB, and I get ~4.5" from pin C/L to spindle hole C/L. I think your cover must be from a slightly later lathe? As for your other differences, it looks like SB changed a number of details on the 9 Jr during the 1927-1929 period. I expect some of those were short lived. Oh, and the casting number on my bracket is the same as yours.