For a race only truck you could probally get away with it. The prob is a dd truck.. you need a large heat exchanger because once that water is hot and heat soaked theres no way to cool it. your just recycling hot water through your a/w system.
Would a heat exchanger be needed if you had a big enough reservoir? Say a 2 or 4 gallon tank?
How about going to a big heat exchange and eliminating the reservoir? Then just surrounding that with ice when you pull or race?
Sorry for all the questions just trying to wrap my head around it before I design something.
I have actually been finding Mini Cooper radiators are a good size and would have room. Just have to make sure they hold the water pump pressure.