I didn't mean to offend you, the part about getting a "cheap" tranny was an observation. Cheap and good are generally not bed partners.
Yes I have been to the track but just not in a 4x4 I guess.
If you are running a 12-14 psi rad cap you can run up to 225-230 without being in any danger of damaging something. On our dirt cars we usually ran a 22 pound cap and considered 250 to be shut down temp but if you were in the lead and got the white and it was on 250 you would stay on it for sure.
I think every 1 psi raises the boiling temp 2 degrees, can't remember for sure.
Also consider the coolant. 50/50 mix is the standard but water has better thermal conductivity that antifreeze, but then antifreeze has a little higher boiling point. We have used a water wetter agent that breaks down the surface tension of water and lets it conduct heat better on race cars