I just realized: my K2 is 41 this month! Build date 11/71, one of the first 800 sent to the States. Has the (leftover) K1 engine and carbs (w/110 mainjets), forks, brake stuff, wheels and hubs, but has the K2 taillight, dashboard, chrome fork ears, and unique K2 instruments (1 year of production), and the 18 tooth front sprocket (which was when that started). Has the K0/1 rhino horn steering top tree and lighter K0/K1 lower tree. Bought it new in 2/72, rode it home 3/72 after my friend at my former Honda Shop employer assembled it out of the crate for me. (I was in college, 80 miles away, at the time, didn't get to put it together myself.)   
Darn...
By about 3/72 build, the K2 had become all K2, with the stamped-steel instrument mount on the non-rhino top tree, heavier lower tree, different clutch internals, slightly longer toe tab on the centerstand (for easier lifting), less cam lobe lift and duration with 657B carbs and 105 mainjets, and the K2/3 spark advancer to match the pipes better and improve sparkplug life. The early K2 had been a plug-fouling SOB, only getting about 1000 miles per set of sparkplugs! The later K2 shifted more deliberately, less like the K0-K1 tranny, too.