Well I can continue to have additional thoughts after sending you messages. I happened to think, my wife had a '72 or '73 250 many years ago. If I remember, it had two, two barrel progressive Zenith carburetors. Is this the same arrangement as yours? If so I have a Haynes manual somewhere covering that car. I don't remember if it covers the carburetors very well. I do remember that the carbs were extremely difficult to remove, but reasonably straight forward to overhaul.
Let me know if this the arrangement you have, and I will try to do a little research for you.