K2 was when the headlight ears came in chrome and the headlight bucket in black, and idiot lights on the handlebar. Idiot lights on the instruments, headlight bucket and ears painted in the bike color, is K1 or K0.
Hmm.. Mine might be kind of a mutt then.. 
The headlight ears are chrome. The headlight bucket is painted to match the bike, but that is irrelevant as the bike was repainted a looong time ago to match the sidecar with some custom pinstriping. Idiot lights are in the instruments.
Being so late in '71... would it be possible that used up remaining K1 stock while at same time using some of the newer K2 stock when they built them?
I am a total newbie to vintage bikes.
Those instruments are K1, no doubt of that. K2 started the "dashboards" on the handlebars. Your engine and frame is K1, too. The pipes: well, they were originally HM300 style, but those rusted quickly, especially the #2 pipe when the drain hole plugged up with chain lube gunk. So, you may have the HM341 pipes by now, which came out on K2. You probably have the better-breathing, earlier-style airbox, which has a wider inlet vent across the back side than the K2 and later boxes had.
The headlight parts: since these got damaged every time a bike fell over, they were often replaced with whatever could be had quickly. They also rusted fast on the earlier bikes, and owner would come into our shop(s) and order the newer chromed ones to spruce up their bikes, so that's a poor indicator of vintage, too.
One thing you might look for on those K1 frames: there should be a small drain hole on the bottom edge of the frame, near the sidestand on the left and near the footpeg on the right. Some had holes in other points along that bottom run of the frame. But, some K1s did not have these holes, and the frames rusted internally, causing big problems. Look for your holes, especially if the bike's been painted, make sure they are open. If not there, drill a 3/32" hole in these locations, or you will get a rust-damaged frame from internal condensation.
Honda very quietly had their reps come around and tell us this in the shops, without publishing it, and we did find a number of K1s that needed (and got) these holes. I have seen rust-bent K1 frames in the boneyards, died from this problem, no doubt.
