I think the Rochester Model B was what came from the factory. As Wrenchbender says, you can ID this by counting the number of machine screws holding the top coverplate onto the bowl casting. Rochester B's have 4 screws, roughly in each "corner."
It is possible that it isn't stock. It might be a Carter YF-type if it has 7 screws holding the coverplate to the bowl casting.
Does it have manual choke? A picture would help. You've got some mighty talented folks scanning these boards- I'm sure they'd be more than happy to help if you provided some info on what you have.
Bill
