Steve,
The IB tractors before 1946 did not necessarily have the C channel frame, it was optional. If your tractor's S/N falls before the IB dedicated range which started at IB1001, it would have a S/N interspersed with regular B production serial numbers, as would the orchard B. If your B has a foot throttle, a parking handbrake and a straight, non-adjustable, solid steel (not tubular) front axle, it is probably an IB. It might still be an orchard model, but based on the info I gleaned from Guy Fays book and Terry Dean's data book, this is the conclusion I came to. Of course, you might also have a regular B that someone has modified to try to make it look like an IB or an orchard B or even to try to make a few more bucks by deceiving an unsuspecting customer.
Let us know how this comes out. You've piqued my curiosity.

Phil

This tractor has a "B" serial number. I don't have the number at hand,but I do remember that it is a 1948 model. I think everything is orginal. This tractor was parked in the woods on my property for more than twenty years. The previous owners son was sure that it had been at least ten years before this since the tractor ran. The previous owner used it as a garden tractor due to twelve children.It doesn't have foot throttle,parking brake,or straight axle,but rather the common wide arch axle.It has a pan seat,correct over size tires,electrics,extra heavy rear axle housings,pto,hydraulics,belt pulley,no shutters,but it has thermostat.Can't be sure about muffler,this was powder after thirty years. THANKS for feed back Steve