Attached photos show a similar stamping under the partial VIN on the firewall under the blower motor on my '69 RS. The first pic, for reference, shows the bottom of the hole on the RH side of the firewall for the blower motor, the partial VIN, and this stamping: K 49 2 under the partial VIN. (Both are upside down in the first pic.) The second pic shows a close up of the K 49 2 stamping.
I asked the same question to two CRG members via e-mail, not through this forum, a couple of years ago. Following is the responeses that I received.
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.
I have been subsequently told that the K may have meant a sheetmetal stamping plant in Kalamazoo, MI.