An Allis C will have a bench seat and will be approximately 45 inches between the rear "drop-down" final drives. An Allis B will also have a bench seat but will be approximately 33 inches between the rear "drop-down" final drives. Both tractors have 3 speed trannys plus reverse. The C is usually narrow front end but could be had with an adjustable wide front. The B was always wide front - either adjustable (like the C) or a fixed arch.
An Allis CA will have a 4 speed tranny plus reverse and a "pan" seat on a shock/spring assembly. If the seat on the tractor is a "pan" seat and is off-center to the right you might have a WC, WD, or WD45.