Based on my experience with 77-78 CB550K carburetors, I think there were minor differences in pilot jet sizes and float heights. For instance, the PD46A vs PD46C carburetors have different factory specs. There is a chart that TwoTired was putting together on the site somewhere. Maybe available in the Carbs FAQ?
From my memory, which is probably flawed, I think that the 78 carbs, although identical castings, had larger pilot jets (42's vs. 38's), but lower float height (14mm vs. 12mm, where higher means lower float - measured upside-down, remember), or that might actually be reversed. There is a lot more information about the 77 and 78 CB550K carbs in this thread:
http://forums.sohc4.net/index.php?topic=22036.msg258435#msg258435