or just have the front 4 points attach straight down and cut holes below where the plates go. Lower the whole cage 6" or so inside the car, weld up all the stuff around the top hoop and against the chassis walls. Push the cage up to its final height, slip the plates under it and weld everything to the chassis via the plates.
There's a couple ways to get it done.
Later
"If A equals success, then the formula is: A = X + Y + Z, X is work. Y is play. Z is keep your mouth shut." - Albert Einstein
When was the last time you *really* did something with your Z to call yourself a Z enthusiast?