Paul, the army census number was painted on the doors. This number had nothing to do with the motor or chassis numbers.
I picked up my 2B1 box today and am going to use it on this cab 13. I have several period pix of 2B1s on cab 13s so it'll be right for this early of a cab 13. The natural question to ask, therefore, is when did they change from the 2B1 to the 2C1?
I traded a rough 2C1 for it so I ended up hauling boxes on my trailer behind the S10 for over 200 miles. There was about a 60 mph cross wind all the way so it made the little V6 earn its keep.