It's a BN model. The N seems to signify a single front wheel. Unfortunately the fellow we purchased it from had filled the cooling system with straight water for a test and forgot to tell us and the first winter we had it froze and broke the crankcase and rusted the internals solid!!! I've got the original owners manual and it's very entertaining to read. Someday I'll pull it apart and repair it. They're great old tractors. MarkNice bike you have. Is that an A or B JD back there My dad has a 46 A my grandfater bought new.
Here's another shot of it behind my TT600