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It looks to be a Speed Demon
With the butterflies showing 1.69 I figure that to be 1 11/16".

I have the chart showing 1 11/16" vacuum sec. being either 650 or 750 CFm depending on venturi size.
650 is 1.28 and 750 is 1.40 venturi
Boosters are downleg
650 is .140 750 is .160

I hope this helps.
Mark



So I found an identification chart on the Internet. A small number 6 is cast on the top of the carb meaning it's a 575 or 650 speed demon.

It's a 575 if the booster is annular. It's 650 if it's down leg. So it sounds like it's a 650.

What does each type of boost Venturi look like?