Eric Cobb at
www.ecob.net makes a good airbox. He is a good information source and flys a Long Ez. Anytime you need a mission, let me know and we can fly down to IZA and see him. He will help you alot.
Regarding your RPM/Prop. Your prop should allow you to run full throttle at your target RPM while still getting acceptable climb. And since your top speed/RPM changes with airframe clean up, everything you do will add to that combination a little.
Gary Hertzler is also very good at airframe efficency and builds a damn good prop. He also flys a very nice Vari Ez.
While you are breaking in, look over the airplane carefully to see if there are any items hanging out in the wind that you can clean up. For me, something as easy as lowering the wheel pants added 2 or 3 kts to the top speed. (this was a Hertzler suggestion)
Steve in KFalls