If it has HM300 pipes and they are the original, it is a K1, not a K2. The first digit of the engine and frame number will be "1" if K1, and "200xxxxx) if K2. The K2 was manufactured starting in late Fall of 1971 (I have one of the first ones to reach the USA), using largely K1 parts but with the K2 "dashboard" on the handlebars (K1 has the indicator lights in the instruments instead), the larger taillight, higher-rise handlebars, the locking seat, and the unique K2 instruments, mounted to the "rhino horn" top triple tree. The seat, if original, will have a bead on the top piece that drops down where the rider's thigh engages it, and the seat foam is narrower at this "saddle cut" by nearly 1cm as measured across the saddle at that point. This was the ONLY bike with this seat, and it stopped before the K2 did, in May of 1972 production, for the K3 (cheaper) seat. IMHO, the genuine K2 seat was by far the most superior seat of all of the 750s...1000 mile days were no problem with it, did many!
The carbs will be "657a" marked on their front ends, too, and will have brass floats. If it is K1, it will have #115 mainjets (if OEM) and if K2 it will have #110 mainjets. The air screws in the carbs (if OEM) will have tiny holes in their tips. The kickstart arm will have a very thin rubber on it, and the shift lever will be very smooth and chrome on the outer side, and the inner side will be almost as smooth (but not sandcast-looking), but not as well chromed.
Finally: the right-side rear engine case bolt, barely visible through the oil hoses, will have an oversized-looking washer on the bolt if it is a K1 engine (or K2 early), with the OD of the bolt looking to be too big for the bolt, but the hole is the correct size. This went away in about March of 1972 in the K2.
A K1 or early K2 has Stellite valve guides with no seals on the intake guides, instead they are longer and have pointy, tapered tops. These are impossible to see in the assembled engine, though...they last for 100,000+ miles, too.
The front forks will NOT have the stepped-in, thin-looking lower legs: they have a slight thinning taper just below the fork boots and inside those forks are some massive brass bearings. These are the tunable (and rebuildable) forks, and are desirable, IMHO. If K1, the fork ears will be painted and rusty: if K2 they will be chrome and rusty on their inner sides where the chrome did not reach.
Value: a pristine K1 could bring $10,000, an early pristine K2 might be considerably less than that, as there were many more of them.
