I would
1. Mark the original alignment of the parts, then bevel the round side of the guide tube. about 3/8" would be good
2 measure the ID of both sides, locate a piece of 4140 shaft material with about 0.005 clearance in the bore. I would want it about 6" long
3. mix up a big batch of that JB weld, coat one end of the 4140 shaft and inset into short (clamp face) side.
4. Coat the second end of the shaft and inset the shaft up to the break surface, maintain shaft alignment.
5. Preheat the casting, then have someone skilled lay down a nice 3/8 fillet in the 3/8 bevel.
6. grind to fit.
7. test
8. quit doing what ever broke it.