[barrelnose]

Also a later post from the carb specialist, and it does have the adjustable main jet,,

Barrelnose - some of the M/S aftermarket carburetors, while less than ideal in either design or quality of materials; did feature externally adjustable main metering jet(s), which might appeal to a racer.

As you say, we will never know. As he retained the unit, we must assume he was happy with it.