[Jeff Lee]

No response on securing the seat back to the roll cage / bar cross bar yet? Is it too simple?
All you would need is a 2" wide nylon webbing with a pair of metal ends on each end. Both with bolt holes in them. Something like the crotch strap found on your 5-point harness. Simpson or somebody could make them for you tomorrow afternoon.
Place tabs on the cross bar, one on each side of the seat set at a distance to allow a tight fit of the webbing against the seat back. Somebody will no doubt have an idea on making the webbing adjustable for tension. Your already supposed to have a method of securing the seat back to the roll bar, this just enforces it.
Confirm or petition with NHRA that you can replace the seat adjuster track with a pair of CM stands which the seat is bolted to and the stands are welded or bolted to the floor with appropriate bracing under the floor as in a roll bar installation. A chassis shop will have less than 2 hours into this.