The scratches if not too deep can be removed by using Autosol(even cheap toothpaste/powder) followed by Brasso or T cut.
It would be easy to do if you had access to a buffing mop on a bench grinder or lathe. Or maybe even a hand drill attachemnt.
Doing this by hand only could take a while but it depends on how deep the scratches are.
If too deep the brush may have to be mounted on a lathe and the scratches turned out,tricky with the knot glued in,but possible.
The uneven base will need to be turned flat or a small base/plinth can be turned for the brush to sit in.
regards, beejay