I just found a really nice 12" Cushman 4 jaw for $120. I'd be happy with a 4 jaw. That diameter damage won't bother anything. Just need to face the shoulder.Great picture there. That flare on the flange and the galling(?) damage are dramatic.
If the spindle bearings are (or get to be) in good shape, you could cleanup the OD (just enough to be certain of minimum TIR) and sleeve any backing plate/chuck for a match fit.
Just thinking out loud.
That is pretty cool but I don't think I'll be switching between chucks. A bit of clearance won't bother the 4 jaw.Could you use some liquid shim? Build up the spindle, machine to size. Worked good on H-53 combining gearbox mount pads.