Here is some information I have come across previously;

"Model Series designations for 1960 were completely revised. The new system began with a letter prefix. For example, a "C" prefix indicated a conventional cab; a "K" indicated a 4 wheel drive model; a "P" model was forward control; an "L" was a low cab forward; an "S" was a school bus and an "M" was a tandem.

A half-ton pickup was now either a model C1404 or C1434. The "C" designated a conventional cab; the "1" half-ton; the "4" a 6 1/2-foot body and the "04" and "34" were for Stepside or Fleetside body types."

The apache name was a carry over from the 58-59 models and was dropped completely for the 1962 model year.

Hope this helps.