As for the round ports not making any more power with carbs bigger than 38mm
Thats not taking into account that the round port head can flow much more than
the 38mm can supply in a hotted up engine or one in a bigger capacity a14/15 etc.
The fully ported round port heads are know to have made 120hp in an A10 for race.
This is not taking into account that Austin A series cast iron heads flow less and
can make 150hp in a 1380cc engine. The Nissan round port head is well underrated.
Ive seen heads with the same sized ports on much bigger capacity engines.