Tow Rig Radiator Replacement

[72-c20]

My '72 K20 is going to become my limited use Tow Rig when my Yukon goes away, and I want to make sure it's up for the task radiator/cooling wise...

Has a new crate 350 (250hp), and a TH350 trans, with cooler lines going to the Radiator.
New Heater Core, t-stat, and Rad cap just installed.

Appears to have developed a leak in the radiator now.

Towing duty for this thing will be maybe a few times a year, with a flatbed trailer and my offroad rig.

I am considering adding a Vintage Air type set-up eventually too...

for the limited towing I will be doing, should I get an external tranny cooler?
not sure how many core rad I have right now, but it runs cool all the time.

thoughts?