Happy to say I found the cracked off mount! It's a single hex bracket that goes into the drum. The correct hex arm is a single that splits into two on top, but I'm thinking of just getting a single arm since I never play it with both toms anyway. I've tracked one down at a local music store, they're not too hard to find. Lots of companies used the hex arms, as you know, but I wanted the bracket to be the correct Japanese one.
A question for you, however, I'm in need of 5 bolts for another President kit I have. I'm looking for either wing bolts or drum key bolts with the old 60's Japanese thread, the same diameter as the modern 1/4" ones but a thicker thread. Might you have any of those?