Nice Mustang. Love the black interior. It gives you a lot of choice when choosing an exterior color, vs. other colors that are more limiting. Also nice that you have an original V-8 car. There were lots of 6-cylinder cars built in '66 as the Mustang was so popular that Ford had a hard time building enough 289s to meet demand. Ford even built the Sports Sprint (to celebrate the millionth Mustang built) package to sex up the sixes.
There were only two engine sizes available in '66: 200 and 289 cid, with three versions of the 289 available. The C code is 2 barrel (regular fuel, 200 hp), the A code is 4 barrel (premium fuel, 225 hp) and the K code is the solid-lifter "High Performance" (271 horsepower). The 200 code is T.
Shoot a photo or jot down the codes on your door data plate (the VIN is also stamped on the top of the left inner fender, usually twice) and I can decipher them, if you've not done it already.