Aha! It's all starting to make sense now. That's actually kind of clever.
You need some kind of brake in order to tighten the draw bar. I suppose you could use a pin spanner that fit into the sockets of the cap screws in the top plate, or the dowel pin holes if they're below the surface. Or drill two more holes. But then you need two tools to tighten it up.
Whatever material you start with, when you turn it down to fit the bearings leave as much radius at the transition as you can to minimize the stress riser. The sharp inside corner is why it broke.
So you need to decide whether to keep the existing setup or fabricate a new brake ring, which is ductile iron. Like I mentioned, I had to silver braze the two pieces of mine back together. I'm sure it broke on yours too, but the previous owner came up with a different scheme. I think they all break eventually because Clausing made a flexure opposite the brake handle by drilling a small hole and opening a slot on the inside edge. Another stress riser caused by too small a radius. It would have been much better to mill a 1/4" (or larger) radius bite out of the ring. Or two. Or three or four. If you decide to go that route and do away with your extra pulley piece, I might be persuaded to do a drawing.
-Jon
