Thanks man.

I sealed it up with the flat surface and annealed copper just fine but I woke up with this idea- a grade 8 bolt should be plenty hard to cut soft cast iron. A nice fitting pilot shaft chucked in a drill welded to a chunk of grade 8 bolt cut lengthwise and a few threads left on the bottom to cut the grooves would probably work great. Oh well glad I didn’t have to make it.