Opinions required please.

[MattF]

If your cooling system is working correctly the bottom of your rad will be cold any way, so putting a manual rad and a seperate oil cooler is not a problem.
I did this on my 2.4 and had no problems even when towing a large trailer with another surf on up some very steep hils.

It'll not be cold, just cooler, around lukewarm. Cooling with an external ATF
cooler, even under load, isn't the problem. As you obviously know, choosing
the correct size cooler and siting it correctly will keep the ATF fluid cool.
However, my point was that neither do you want the ATF fluid TOO cool.
That's why not passing it through the rad cooler would not necessarily be a
good idea. An external ATF cooler alone can only control the upper temperature.
It has no way of controlling the low temperature range. As with the engine, the
auto box has an optimal operating temperature. That's why even race
cars have a thermostatic switch to control when the fluid gets passed to
the cooler. However, unlike domestic vehicles, they will never be stood for
periods of time which would allow the ATF fluid to cool down to any degree,
so overcooling doesn't arise in that scenario. Domestic use, however, it can.