Jeff,
I am not aware of any internal adjustments (or any other turn-screw adjustments for that matter) that would effect only a specific RPM range. I've heard early racers would substitute different shaped cams to get better performance at different RMP ranges to give them advantages for passing on certain tracks but as far as I know that type of "adjustment" is way, way beyond what a "duffer" should attempt.
I second the advice to get in touch with Gus at:
Pacific Fuel Injection Service
153 Utah Avenue
South San Francisco, CA 94080
(650) 588-8880
If anyone would know, he would. Perhaps Grady Clay will see and respond to this thread. He's got more MFI knowledge that the rest of this board combined! If you figure this out, please post your conclusions.