I cant tell you the length but can say that I have used what I think is a plunger lower yoke with a s/a upper and the only difference is the steering stop locations, the overall length would be much the same, or at least nothing obvious to my assembly - BUT I have used rollers ilo balls in the headstock which separates the yokes a little more, but the divers helmet still seems to fit ok....are you sure you have an A series shroud? I seem to remember somebody had an issue like this on another thread and it was suggested it may have been a C11/C12 shroud......