Are you planning to press in new bearings? This tool is for doing that. If you're just removing the yoke/stem, you don't need it.
You won't be able to weld that back on. You may be able to build up the area with weld and machine it afterwards but with the slot that won't be looking great either. That's if that material is weldable. Cast ir forged aluminium is mostly of a non weldable composition. You can stick it together for non structural stuff but there won't be any strength. I do quite a bit of aluminium welding although as a hobby. I personally wouldn't touch that.
