Paul,,,,
The 'first' carbs used on the 383/343,
Front carb #2790, and back carb w/choke #2791
1 7/16" Primary / 1 9/16" Secondary
1.063" Primary Venturi / 1.125" Secondary Venturi
And,,,,,,, Mr. #3258 and #3259,,,,,,,,
1 7/16" Primary / 1 9/16" Secondary
1.063" Primary Venturi / 1.250 Secondary Venturi