That is a good tip for the Rad support. I have several old Jeeps so I just swapped out the support. Either will work fine.
I will comment on the idea of cooling the tranny thru the radiator, and again, people can take it for what it is worth.
According to Allison, and their specs and documents, preheating of the fluid(assuming Dexron III is used) is not necessesary above -13*F. Even running 15/40 in the transmission will allow temperatures down to 5*F without preheating. Unless you are running straight weight oil, heavier than 30wt, then there is no need to preheat the oil in TN. I didn't just pull it out of my arse, I have the paperwork and documentation to back up everything. Additionally, Allison calls for a maximum pressure drop across the external coolers/filters, of 35PSI. Now, I don't know what the drop would be, using the tiny diameter cooler in the radiator, but I know that added to an external, and a pair of external filters, it is going to be more that if it was plumbed as it was designed to be plumbed. Personally, my choice would be to minimize the restriction, using the largest filters and coolers possible.
FWIW, the data I quoted is real, it is free, and it is available on Allison's site.