I've currently got my seat out for a gas tank replacement, and I keep eyeballin' it trying to think of an easy way to add a little more rake to the back. Just a couple of degrees would yield not only more room but greater comfort for those of us who like to slump a bit behind the wheel. I guess in the old days they spent more time sitting upright in a proper pew, so seats like this felt right :-D
You’ll only worsen the problem by adding rake. The original seat back configuration, slid all the way back hits the cab back already. If you rack the seat back the seat bottom will be closer to the steering wheel.
The only way to gain any room is to remove cushioning/springs, replace with more modern seats or replace the steering column/wheel with something smaller.
