first i'd try

taking out the seat and check if you sit all the way back or if just lowering the seat/floor will do the trick. If you are going to be on a track, then you will most likely not fit with a helmet without getting yourself lower. Also take in account the seatbelt positions if not planning to use a harness. I know on late models the retractor is behind the seat somewhat and mounted to a pretty sturdy point. Someone may know if there is any structual parts that may hinder moving back into the fuel tank area. You will most likely be resting your head aginst the rear window if you are able to move the seat back more also. X seats are remarkably thin as it is. you may want to try getting another stock seat and modifing the seat foam to sit lower and back more. I found most thin racing seats are pretty close to stock x seats for the height you sit at. I'm sure others can confirm this. It will all depend on if you have long legs or torso. Lowering can remove the steering wheel conflict and you can also change the angle of the steering column to help some. There was a writeup a wile back, should be able to search archives.