I have always ran a cooler in the past. Heat is the #1 killer of an automatic transmission. Depending on what you have , you are most likely fine with one from the parts store. I personally use the biggest one I can fit. Some people use the zip tie style of fastener that goes through the fins of the cooler and then the fins of the radiator.I guess its ok, but I just don't feel comfortable going through the fins of either. I usually fab up some kind of bracket with a rubber covered clamp that goes around the tubes on the end. The big thing to remember is to use transmission cooler hose instead of rubber fuel line. There is a difference.
1969 x-77 Z/28 orange/ white stripes, named by my daughter "Clementine ", M-22 close ratio, 4:10 12 bolt, CE 302. Hugger orange with white stripes. White standard interior. Restoration complete May 2018