I think you're probably deluding yourself mate, what you've got there is a "bitsa", i.e., it's made up of "bits of this, and bits of that".
Your bike had probably been "down the road" like most CB750's have been at one time or another, and the original K1 gauges have either been smashed or removed for some other reason (sold, used for another project etc) and someone's put K2 gauges back on, and with your mis-matched pipes, either they've been damaged or rusted out, and have been replaced with whatever's available.
Good thing is, the K1 is becoming more "collectable", and the parts that you need to make it right are still available. Cheers, Terry.