Let me begin again saying this is an excellently done diorama!
As far as the B and C Farmall goes there are some easily notable differences. The A, I-A, Super A, B, and BN were known as Cuti-Vision tractors. The driver seat was to the right of the tank and engine and the steering shaft ran down the right side. These tractors also had drop type or reduction gear axles in the rear, with usually 24" rims. I still have a 47 I-A. The C and Super C wasn't made with the driver seat mounted to the right, and the steering shaft ran down the left side. The rear axles on the C's were not drop axles either, they were direct with larger rims, looking similar to the axles on the H and M. Here is a picture taken by someone else of a C that belongs to someone I know taken in 09.
Southeast Old Threshers Reunion Denton, NC July 1-5, 2008 031 by jdrammer, on Flickr