From what I have seen over the years I came to believe that Hitachi did a running change on the carbs in 1973 where the round top carbs got square tops without changing anything else that I could see. These were still secured to the standard 1200 GX manifold.
I remember seeing these carbs in a few photos in the last couple of years.

The next development was to change the main body of the carb for the polution functions. The carb linkages are unique to the A series engines, including the throttle shafts so carbs from any non A series engine would need to be rebuilt with the correct GX type throttle shafts to work on this manifold.
What do you think the chances of that are.

I'd say that someone pissed before geting it out of his pants with this thread.