HHMMmmmm!...... Not sure to be honest, but I think the 'b' was the first in the family and would have had some components and layout from the earlier -22b. There were a lot of mods done to the engine fuel system, gear box and oil system!
FYI the b3-02 was an interim development and ordered by PAN-AM.
It may be a historical thing and I would think that by now they would all be to the same mod standard.....but I may be wrong!
Pratt and witney did much the same with the JT9D It started life as a -3a then -7 -7cn (converted -3a) -7a and the list went on!!