My take on this is , first , the cooling lines in the rad. are too small ! Second, why don`t u just wrap the header in that location, and wrap the oil filter itself. I have been wrapping my starters for yrs ! Have never lost one yet .
I agree that the trans cooler in a radiator probably can't handle engine oil pressure. Just saying there may be some advantage to more equal fluid temperatures. Toyotas engineers thought so.