I own a 680C (1974) and have not found anywhere to determine the year of manufacture by using the serial number. But there are ways to determine closely the year of mfg. Such as what kind (gas or diesel) and size is the engine. Does it have air brakes or mechanical ? Quite a few changes were made to the tractor from the earliest to the last of the 680 series tractors. You say you ordered a shop manual for it. How did you know which one to order ? Did you use your tractor serial number ? If you prefer to not post the serial number in the public forum, PM it to me and I will do a little research on it. Actually I never heard of a 680CK B model. That is why the serial number is needed.