I found a Mallory 1B8R here: https://www.antiqueradios.com/...hp?f=15&t=336750.
The ad below the picture of the rectifier makes it appear that model numbers starting with 1B8 have eight junctions (says the 1B8R has 8 junctions instead of 4 like the 1B4R above). I am wondering about the eight junctions.
Although these pictures do not specifically show the Mallory unit, these Ebay pictures will give you an idea of how they looked. Basically square heatsink fins, the higher the amperage, the bigger heatsinks. The seleniums were not terribly efficient and heated up..
The eight lug rectifiers were either connected in parallel to increase amp rating or in series to boost the voltage rating with addition of high resistance resistors to even out voltage drops so one pack was not overloaded.
Oh yeah, forgot to mention, you did not want to be around when they fail. Cross between an outhouse on hot day and worst rotten egg (hot sulfur) smell. When younger, I had a small Lionel HO power pack (red lever that went right or left for train forward reverse.) It suddenly and dramatically failed with smoke and rotten egg. Couldn't sleep in my room for several days and kept windows open 24/7 until stench abated. Ah the memories.....NOT!!