RE: Filling the tank with the cowl on
Peereback,
I don't know if your question got answered, but you need at least two lines running to your tank, regardless of whether or not muffler pressure is used. If muffler pressure is not used, then you need a vent line that will purge the air as you fill the tank, and will allow air to replace the fuel once the motor starts drawing it out. Without a vent line, your setup will never work. Simple physics.
In your case, I'd hook up a vent line (connected to a brass tube leading to the top of the tank--as if you were installing a pressure line), and then just run the end of the line out the bottom of the fuse somewhere it's not so noticeable. Fill the tank until fuel runs out of this line, and you're full!