I recently did some code searching of my own. I hope the links below help with your research
http://www.mustangsandmore.com/ubb/Forum7/HTML/000506.html
http://www.classicmustang.com/casting_numbers.htm
http://www.gearheadracing.com/Reference/Ford/CastingNumbers/FordCastingNumbers.htm
http://www.mustangsandmore.com/ubb/Forum7/HTML/000506.html
http://www.classicmustang.com/casting_numbers.htm
http://www.gearheadracing.com/Reference/Ford/CastingNumbers/FordCastingNumbers.htm
C code 200 hp, A code 225hp, K code 271hp, S code (390) 320hp. The K code has solid lifters, higher compression heads, better cam, more free flowing air cleaner and exhaust, something about the valves ( I can't remember)maybe chrome plated stems. There are a few more things, suspension stuff was different and 9 inch rears. The C code is a 2 bbl carb and the A is a 4, also the heads must be a little different since the C code has 9.3:1 compression and the A is 9.8:1. The K code is 10.5:1.