Doug67 is correct. To continue answering your question, the 2+2 designation was used in 65/66 (there were no 64/12 2+2's) and wasn't used afterwards. You won't see a 2+2 badge after 66.
The "K" code is the engine code for a 289 HiPo. A "K" code could be ordered in a coupe, fastback (2+2), or convertible.
The GT package, only offered after about the first year of production (i.e., 64 1/2, early 65's can't be "true" GT cars), was only available with the "A" code 289 4V and the "K" code 289 4V HiPo. The GT package could be ordered on a coupe, FB (2+2) or convertible.
I was always told that it is not 2x2 unless it has the fold down rear seat. For instance, my 65fb is a 2x2 because it has the fold down seat...but my old 67fb is not because it had a stationary rear seat.