All the computer has done is picked up 20. This is one of the problems with all computer systems, google a part number and it will show pictures of a different part
The UK K2 is one of the honda's that i specialise in and have wrote many times about the frame, engine number differences and the fork differences that are fitted. Some years ago i bought a UK K2 1973 with VIN 20 and engine 22. The vendor told me that he had looked up the numbers on a USA site and the bike had a K3 engine fitted at some point and, this is why he was selling it cheap. Who am i to tell him that it was the correct numbers
I wrote this some time ago but, it will give you a idea on the UK K2 numbers >>>
In the UK we never had K3, K4 or K5. It just stayed at K2 so even if you have a 1974 CB750 in the UK the frame number sill started with 20...... but, the engine numbers carried on as they did in the USA.
I have 3 CB750K2's at the moment and here is a example of the way the numbers went
1972 CB750K2, Frame number CB750-2050308 with engine number CB750E-2058045 >> manufactured late 1971
1974 CB750K2, Frame number CB750-2084102 with engine number CB750E-2256216 >> manufactured 1973
1975 CB750K2, Frame number CB750-2086882 with engine number CB750E-2307782 >> manufactured mid 1974
I have also just sold a 1972 K2 with the engine number lower than the frame.
If you have a very early K2 VIN number, it could have a K1 engine number but, i have only ever seen these in Japan or the USA
