I've done some soul searching and decided to send the bed for grinding. Since I've done so much hard work scraping everything else in I couldn't leave the main bedway in any doubt, expensive as it is to have done. Once that's ground the lathe should work literally as good as new, with the additional benefits of thrust-bearings in the cross slide and the large dial it should actually be better than new.
I've also given up on the idea of trying to reproduce the lathe's data plates and ordered some reproductions from a guy in America. They are beautifully made and the time I would have to invest to do half as good a job doesn't make any sense.
Out of curiosity, what sort of money is required to regrind a bed?