If you remove the center bolt and drill 2 new holes it can remain right there as a fixed base vise.
Or if you really want to go for it, I would use bronze-brazing.
Ideally you have a gas grill, oxyacetylene torch, and some flux coated bronze-brazing rods.
V-out the cracks top and bottom with a file or grinder, fixture to lightly hold back in place with steel blocks. I would preheat the whole thing on the BBQ to save on oxyacet gases.
Melt a little flux, eventually with heat the braze will flow and wet the cast iron. Don't expect it to wick like soft-solder does into a copper pipe fitting. It just sort of sits in the V, work from one end to the other. Then you flip it over and braze the other side, sort of trial and error with heat to keep the top work from dripping out. But if it does, just go back and braze the other side.
Here's a cast iron pedal I fixed for a press brake. You can see a little drippy spot on the top where it needs more work.