Have you tried contacting Vermeer? If there is no local dealer, try their website at: http://www.vermeer.com/
Their phone number is 515-628-3141
I believe the 630B was a later model, with improvements over the 630A, but I'm not sure exactly what the differences are. I think one change was going to 8 cutter teeth on the 630B as opposed to 20 or 30 on the 630A.
we have a 630A and as far as i know it is the same as a 630B except for a B may have wider tires, and it does have fewer cutter teeth and they are the newer style teeth, and it may or may not have tail lights. but as far as engine and hydraulics i believe that they are very similar. but your vermeer dealer can tell you more than me, i hope this helps.