Strange Carb Numbers

I have a couple of weird questions - the first is about the carb on my '76 KZ400S2...it's stamped  "V5B", with the numbers OC23 and OC19 respectively on each side. I can't find any cross-reference for this carb. Also, the manifold boots for this year bike is allegedly 16065-037, but that number cross-references to a boot that is 5mm too narrow than the ones I took off! The throat of the manifold boot I took off measures 41mm, not 37mm.  Did somebody down the road change out the original carb?? Also, the jets you can see in this carb are #40 on top and #90 below, on both sides...the diagram calls for both to be #40 in the 1976 KZ400S2 - but there IS a #90 listed for the 1976 KZ400D3...
Now, the '76 D3 ALSO lists those two jets as #40 and #40...AND shows the OEM carb as a V5B... but what/why is the discrepancy between those and my '76 KZ400S2? What is going on here...? Is my '76 S2 'accurate'?  Did somebody just change out the jets, and why would they do that...? 
 
 

I do not know much about the 400 machines. but there are several here who do and will most likely respond to this topic.  There is a bunch of info on the 400/440 bikes on KZ400.com.  Things like manuals, diagrams and tech/tips there. This table is from there.

kz400.com/Techh%20tips%20bilder/Tech%20filer/18.jpg