I have a 160 mm version, and am pretty sure I saw a 155mm one somewhere.
The 50.4 mm bcd was common on high end cranks in the 30's, when Stronglight introduced the first cotterless crank. 50.4 seems such a random measurement I wonder if it didn't start out as 2" or something (I know, that would be 50.8 mm...). I have a Constrictor cottered crank that takes that size ring.
The first version of the TA crank had a bizarre spindle that was half round and half square, and took a cotter pin. I used to have one of those cranks, but gave it away. Duh.
According to the BQ article I referred to in my previous post, the design allowed one to make side to side adjustments of the crank to fine tune the chain line. The TA cotter design did not bear the pedal load and only held the crank in place on a pear shaped axle.