Bruce my man.
The A drums are similar to the post war drums but have a smaller bore for fitting over the hub, but then that has nothing to do with water excluders as they are attached to the backing plates. The twin has alloy finned muffs on post war cast Rapide drums as it had in the early 50's on the road in Toronto and it has post war alloy backing plates with no water excluders, all replicating what was on when it T boned an Edsel in 1958 and destroyed the original front end. The TTR has replica composite drums and replica alloy backing plates I believe made in the NE US in the 60's? Again no water excluders. That's the extent of my A front brakes knowledge!