Two steps forward one step back - here we go again.
I tried measuring twice and cutting (er, drilling) once but it didn't work. First I sat against a wall with helmet on then placed a peice of tape on the wall at the top of my head/helmet. Then I added two inches (too much, I'll just be sure to cinch the lap belt) for turbulence. Measured from the top (torque as I think someone called it) tube down to the seat. When it was all done and said I drilled and bolted in the seat. Final part was to confirm what a nice job I did by getting in the seat and verifying it made sense. Nope, didn't even pass the sniff test. No way do I need 6" of space above my head (I'm 5'10") but I do need another two or three inches below to clear the elevator cable (should have installed that before the seat. Ha, Live, Laugh, learn, rejoice, rinse and repeat.