Well actually, I'd get a seperate cooler for the auto box, then you can fit either a manual or an auto rad to the car.
Incidentaly, I have a custom made full ally rad for sale. Totally brand new, never fitted. It will fit the Z32 bit it's a tight squeeze and I'm not quite sure how the fan shroud would fit. Anyway, the price is £200 (of which £25 is currently owed to 300zx.co.uk forum funds, as this was part of a group buy). It is nice, it is shiny, but as it's a non-standard part then you'd probably want to look at it before making your mind up. I'm based in Essex near Great Dunmow, if that's of any help.