Thanks everyone. I think it's the depth of the pitting that has me stumped as I don't know how I would go about 'filling' them with the paint. Maybe just lots of layers over a couple of weeks or something. Or maybe the shellac will even out the surface once I've blacked them in again.
Thanks for the link on restoring the shellac - that's the one I had been reading when I got kicked off and couldn't find it again!