electronic ignition for model B engine?

[DavidG]

You should consider investing in a reprint 1928-34 chassis parts catalog. They are inexpensive and answer all manner of basic questions and provide exploded-view illustrations of many components, including one of a '32-'34 four-cylinder distributor. The answer to your earlier question about the attachment of the condenser to the distributor housing is clear as a bell in that illustration and your current question about A and B is answered by the listing of the individual components and their model year application.