I hope you don't take any of my comments and suggestions the wrong way, I'm want to see you succeed in a safe manner.
I wonder what your rules say about the rad in the cab. Every set of rules I've looked at specify no fluid lines in cab. It doesn't take much more hose to run it behind the cab, and make the line connections face away from the seat as much as possible. Nothing like scalding hot water to take your attention off winning the race. My research has told me to keep the cap or some fill point as the highest point in the system to avoid problems with air pockets and overheating.
I think you might want to add a diagonal to your rear hoop, from top drivers side to bottom passenger side.
As well I would suggest that you raise your shoulder belt mount. You don't want the shoulder belt to compress you into the seat, it's meant to keep you from hitting the dash. Your lap belt is what's supposed to keep you in your seat. There is a good article about this subject in the tech section at Pirate 4x4. do research elsewhere as well, it's always good to have more than one point of view. If you haven't already bought a 5-point harness, I would suggest Hooker harnesses' ratcheting system
http://www.hookerharness.com/racingaccessories.php . It's pricey, but IMO the best bet so far.
Looking good so far, I can't wait to see video of you racing.
Richard