46a would be PD carbs found on the 77 CB550K in the states. The 78's got the same carb style with a slightly different set up ,and were stamped 46c
Most of the Honda documentation showed X46 carbs. I finally decided that was a place holder used by the tech writers. And, it never got corrected/refined before somebody sent the manuscript to the printers.
Who knows, there could have been job reassignment issues, or simply stuff lost in translation. Certainly, the 77 and 78 models were the last of the project line. So, ongoing deliverables got lower priority than Honda's newer models.
Only the fly on the wall knows for sure, I suspect. And it took the info to the grave.
Cheers,
