Seems like a well tune engine to me.
I'd like to see a pull with a smaller carb, maybe a 650, then bigger headers on another.
Laugh if you want but I'd be interested in what it does for torque numbers.
You aren't wrong in your thinking--total air consumption is well under what a 650 will provide. A good 650 carb wouldn't hurt this asthmatic engine one bit. J.Rob