There might be multiple versions of each of those "models"

different types of choke mechanisms

B - manual choke
BC - automatic choke
BV - vacuum break/brake (?) - "vacuum operated diaphragm plunger"

http://carbkitsource.com/carbs/tech/Rochester/B-index.html
http://www.carburetor-parts.com/Rochester-B-BC-BV-Carburetors_c_649.html
http://www.thecarburetorshop.com/RochestermultipleB.htm

big download - 1964 manual that describes the three 1964 models:
http://www.newagemetal.com/pages/ServiceProcedures/B/1964/64ModelBmanual.pdf