If I'm going to swap my stock radiator for one of the universal aluminum ones, how much or how big of a trans cooler do I need to install to equal whats already there? (Stock 700-4 Trans. 95% race track 5% tooling around on the road)

 

You want something BETTER than what's on there if you do 90% race. If you're talking drag race (especially if you do some hot-lapping sometimes), overkill is just about right. Drag racing throws a LOT of heat in a trans very quickly.

I've even seen guys use the old A/C condenser as their trans cooler. Personally, I doubt that an A/C condenser would be nearly as efficient as a cooler built specifically for transmission cooling, I'm just saying I've seen it done and they never had trans overheat problems.