Not sure of B bodies, but on my A there is a lip, about 1 or 1-1/2" tall above the floor of the cowl, for a water dam sort of thing, surrounding the opening for the vent, and mine had rusted mostly away, contributing greatly to the non existant right floor pan...
Not sure how the B is attached, on my A the heater/right vent are attached by(among other things) "J" bolts, IIRC.
If the water is dripping from the inside of your vent, I would look here.