It wasn't a Torx - that's only six sides.
It wasn't a triple square - that has 12 sides and is commonly found in German cars.
It is called a double square - it has 8 sides and (apparently) was common in the 50's.
I set out to find a double square wrench to try to tighten this drain plug up and found that (or didn't find) anybody who had it. I did get a suggestion that totally worked - a 1/2" ratchet seemed to fit like a glove. I've snugged it up and so far so good. Now to get the JB Weld off...