Serials 128001-152777 are, 1930, 8hp
Serials 152778-161326 are 1931, 8hp
Serials 161327-167430 are 1932, 8hp. These are the last opposed “K-” models.
The first “stacked” K-models debuted in 1933 with the K-65 @ 9.2 hp. Racing models were 12hp.
The last K- models were sold in 1936 @ 9.3 hp. A KR-1937 but I don’t know if it was a variant of the K- models or the newer KA- series.
I have a 1934 K-70, purchased new for my family’s Camp Sunnybank in the Adirondacks. It still runs.