Ok so I was able to take a few pics which are not good. I believe the date code is a 1976 soooo not a CKT. My pics are pretty bad but think it is clear enough to put this mystery to bed and say someone prior to me thought they were getting one over on someone else.
My guess would be that someone at the assembly plant grabbed the wrong stamp when that engine was stamped. The list of 1976 codes shows quite a few similar ones like CKY, CKX, CKW, CKU, and CHT. If they grabbed the wrong letter, the engine could have been mistamped.
If you have an opportunity to pull the valve covers, you can get numbers from the heads. Also, a '72 Z28 should have had guide plates for the solid lifters. If the engine has solid lifters, you can hear them when it runs.