ive built a few rollcages for dirt track racing (in holland called autocross), and i can get you a few tips. the tube from the a pillar to the b pillar, get one in the middle, but dont get it on the floor , just stop where the b pillar goes from left to right and weld it on that tube. if you are taller, weld a plate on top of the cage instead of a cross. get a cross welded behind your seat (dunno if you need to get your seat fixed to the rollcage, but whe had to, so, starting from the x between the b pillars is a very solid start. also, make sure you've got a pipe laying on the doorsill, just below where the x is drawn here, makes your cage a lot stronger. cross between the last legs wont help much, use a single tube on the last piece, and maybe to cheat the rules a bit, make the c pillar tubing end almost on top of your shocks, and you can fix your shocks to the rollcage. wheve don the same at the front, and the car went on and on and on and on, for 6 seasons iirc, while much of the other cars did one or maximum two seasons.

i like the idea of the races you have, overhere there are getting way to many rules (even sound regulations), so time for another class!