Thanks Jon.
I realise I wasn't clear - I am keeping carb top, body and correct venturi together, using the assembly that seems to me the better, or more correct, fit.
What I can't be sure of is whether someone has already mixed them up - in both carbs, the venturi has been rotated 180 degrees, so someone's been in there. However, they all appear to be the same design.
Both carbs have what sounds like your second item. The venturi have two ridges, top and bottom, which locate with corresponding lands in the carb top, each with a thin round gasket.
