Joe,
The plane is dam near perfect... Every time you make something a littler better, there is always going to be the next thing that is holding it back in some small way. You are down to splitin hairs, and have been for a while.
If it is running short of breath, it could be the carb bore, or it could be the porting on the heads, or... I'd say you are just about there on getting much more out of the plane...
Except maybe a light weight JATO. :pee: