I don't know if you can do it in your lathe, but couldn't you use an
angle grinder to take off most of what you want removed and then use
the surface grinder? Maybe use the surface grinder to show the high
spots and then hit it a bit more with a flap disc before going back to
the surface grinder.

In any case I would use an angle grinder to remove the surface before
trying the lathe.


Dan