Unless it is a Concours resto you are best to have an aftermarket aux cooler (air to fluid) in series with the radiator heat exchanger. Put it after the radiator, so go box-out (5 I think) to radiator to cooler and back to box. Even a small one helps and can drop your transmission fluid temperature drastically. It is a must if you have any sort of non-standard stall speed too. They are easy to fit with a few handmade brackets to pickup existing radiator support holes.