Dual plane to single plane track test in the works

I got the best power with an airgap and one inch open spacer on a 408. Didn't try a single plane. Cam 235/249/107 EQ. heads, 10 /1 compression.
Max hp 5700 and carried it to 6,000 . max torque 4700. I am betting on the airgap if you use an open 1 inch spacer if you shift at 6200. My guess is it would run stronger with the single plane with more rpm.