Under the outer heater box/blower cover stamped on the firewall of my 69RS were the following. The partial VIN is well understood. I was informed from CRG membership that the K 49 is, as JohnZ has indicated the stamping number. The following is part of an e-mail exchange that I received on the topic.
It's the date and factory code that indicates when that piece of sheetmetal was stamped. In this case the 49th week of 1968. We have not figured out which sheetmetal plant is which, but I've seen H's, K's, and T's on various parts on the cars. The most obvious one is right in the center of the trunks inner stiffener. Those usually begin with a T. If there is a third digit, I don't think it would be a shift number since the stamps only changed weekly. May have indicated which machine or which mold it was stamped in.
The K is a code for the stamping plant. 49 is the 49th week of the year - mid-December, which relates well to your car build date. The meaning of any suffixes isn't sure, but could related to the shift as you note.
Build date on my car is 01C. Subsequent to the information that I received above, I was told that perhaps the K stood for Kalamazoo, M stamping plant.
Firewall pic attached.
