I also thought the intake tract length began at the valve and ended at the carb intake, but Stuart Hooper disabused me of that idea. He told me it ends at the bell mouth and it does not matter where the carb is. The intake is tuned just like the exhaust. The negative pulse in the intake reverses as it moves the end of the bell and turns positive and heads back down the intake tract. The intake tract length needs to be tuned so the positive pulse hits the intake valve just before it closes. The pulse weakens each time it reverses, so the second pulse is the strongest. Unfortunately the second pulse needs the longest intake tract.

To hit the middle of your range using 6500 RPM the second pulse would indicate a 20.3" tract, third pulse 14.9" and the fifth pulse is 11.4". These are just starting points for the dyno work.