2 things to think about on the inlet/outlet size is that a carburetor works off of flow of air...which is created by the vacum of the cylinder on INTAKE stroke. I believe that motor fires in 4 fires, not 2, so only one induction at a time. The inlet being 2" and each carb outlet being 1" means it never needs more than 1" of air at a time.
The second thing, which kind of offsets that, is that you DO want a larger and unrestricted flow before the carb...think of a velocity stack. That is import at WOT where a smooth, high flow is key.
So a balance of the 2 is important and that is calcuable.
People need to remember that in cylindrycal shapes doubling the diameter is not just twice as much....Pi x r2
I do not know the formula for his optimal inlet size, but he WELL MAY be just fine.