If you do any sort of towing or hauling an external tranny cooler is always the better choice over a cooler integrated into the radiator. In my case where I installed an external tranny cooler after the radiator integrated cooler on my truck I noticed a reduction in temps. I would think that the logic of having the oil cooler be external would apply especially to the radiator, on a Z with a cramped engine bay and a hard enought time cooling just the engine.
