I agree with K10. Although with the availability of parts and being able to interchange them allows you to build what ever you desire. I have owned several 63's and know that the parts are harder to find for the 60-63's as opposed to the 64-66 models. I also notice far more fleetsides than stepsides. At least in the south.

http://s971.photobucket.com/albums/ae197/jon63c10
1963 c-10 shortbed stepside 427 BBC T16 HD 3 speed
1963 c-10 shortbed fleetside 348 "w" 1st gen big block & powerglide