I could not find a "B" on the floor plate. However, neither could I get the floor plate off when I was cleaning out the cosmo. Would the brass pin be visible from the top of the magazine looking in?
No, you have to take the trigger guard out of the stock. The pins were horizontal near the floorplate latch area. If it has one, you will see it from the side. Floorplate could also be "stuck" to the TG with dried grease.