Checked my Comm 10, my Comm 10A and my early Comm 12 (all yellow tractors) this AM and none of them have the K-series designation on them. The engines on the two 10HP tractors are designated model #G-24 and on the 12HP machine, model #G-30-E. I forgot to look at my red colored Comm 12 this morning (later vintage - 1974), but I believe that motor does have a K-series designator on it.
If you need them, the spec # on the Comm 10 was 46341D and on the Comm 10A, #46520D. These engines would be equivalent to the later K241 designation and the ones I've observed had an "S" suffix on them, as have the walk-behind 12HP tractors (K301S). Keep in mind that the 10HP and 12HP tractors from that era share the same engine block - with the only difference being the 12HP having a slightly larger cylinder bore.