Brendan - After seeing your reply, I revised my original decoding of the FB offered truck serial number. I should have noted

that the month "number" is represented by the first
2 digits following the model designation using the example in the 3rd picture I posted from the 1940 Truck Data PDF.
I've edited that info in the reply above to show the correct decoding.
For your serial number decode, the "03" after "KC" would indicate the build month as March and the unit number 7241 would indicate it was the 6241st truck off the line in Janesville.
Which leads to another inconsistency. How do you have a truck supposedly built in March with a "7241" sequence number and also have a truck built in November at the same plant with a lower "2651" sequence number? I think the FB sellers info may not be accurate, and the only way to resolve this is to get a picture of the FB Truck data plate so we can see exactly what is stamped on it. Then maybe also a picture of your plate for comparison.
Sorry if this is still murky as mud.
