Hello Harris,
Here's a URL that may help a little:
Draw-Tite coolers
It shows a cooler added downstream of the radiator's cooler if you have one (which I do).
If you only have the external cooler, there are models made by B&M and others with built-in fans that should be pretty durable as they are sold for tow vehicles and motor homes.
I guess you also need to decide how much abuse the trans needs to take
If there's a lot of racing involved you probably need all the cooler-power you can install. If it's 99% Saturday night cruisin', maybe the cooler can be a bit smaller.
Since you are using a fairly high stall converter, my opinion would be to use a bit of overkill in the cooler, as the more stall you run, the hotter the
oil will be.
Hope this helps,
Tom