Ahh a good horizontal mill...
I am not sure how, but I almost missed this thread. I used to use them a lot at Lie Nielsen, that is what they used to open up a few raw castings on some of their block planes (62's) and of course where they milled their shoulder planes and corrugated their bench planes.
They definitely have their place, but while we have an old one at work that I could have, I passed on it. Yours looks to be in a lot better shape even with the damage. I doubt you will have problems getting it back together. They are strong simple mills and you can find cheap cutters all over the place for them.
Good luck in any case.