Couldnt find a 48 catalog but it looks like the very base model - no name. Other models, as they started getting more expensive, added, truss rods, lights, tanks, chrome wheels, chrome fenders, more elaborate chain guards, then there are cantilever frame models. Etc.
But the serial numbers do not designate models. You can start adding options as you find them and "dress" it up a little more. Usually if you do that, you'll spend more piece mealing it together than you'd spend just buying a better equipped one to begin with.