Hi mate Just reading your post and would like to find out a bit more information as it is hard to dignose a problem without pictures.
You mentioned you are getting radiant heat around your transmision area, is this because you have your exhaust pipe running close to the transmition then both exhust pipes conecting into each other down the drivers side?
is your gear box when hot is getting hard to select a gear?
Do you have a picture of the area?
One of the post above mentioned about using heat shield, I would look at using a product called zeo clearance heat shield (it a stick on product), it can stand tempretures up to 246 degrees for a constant 30 hrs.
I would be adressing the issue by deflecting the heat away from what you are trying to protect, there should be enough air flow around your exhaust to cool your exhust. Best way to test is wait till your exhust has cooled down, use a tempreture gun if you have one ( if you dont, wait 1hr then use caution and leather gloves to feel the exhust temp) then feel the transmition area, If the transmition is still hot, then you are getting heat soak from the exhust.
Start with reflective heat shield, if itis still getting hot I would then recommend covering the exhust with exhust wrap only the small section where the pipe crosses over the transmission area.
Running a transmition cooler, would you not use the drain and fill ports as you connection for the cooler then use a 12 volt pump to circulate the oil? Only problem is the oil will take a while to get to tempreture and could do damage to the transmission over a long time as the oil will be thicker, may be look into a tempreture sender like David craig thermal timers, somit pumpsn the oil once it get to tempreture.
Othernissue to consider when using the drin plug as the pick up it will be the lowest point on you transmission and could get damaged when 4wd.