Take a look at the Bachology website and you will get alot of info:
Welcome to BachBrass.com
In fact, they have a picture of a bell with the markings of 26-59 which as stated above is a ML (.459) bore with 26 bell. Bach experimented in the early New York days with many different bells. Perhaps more than 70 or so. NY Bachs are all custom horns with varied bell, bore, leadpipe combos. That is part of their allure. The best thing is that Roy Hempley has access to Bach's shop cards where Bach kept a record of the specs of all of his horns. Mr. Hempley was able to send me scans of the cards of all of my Bach horns (3 NYs and 1 MV).