Cant cool my 5.9 magnum. Radiator size or add one thing else?

Hey all.
I am on my third 5.9 Magnum engine swap into my older 1970 cars.
All of them seem to run fairly hot. I know Australia is a hot climate but they still are too hot. I run a 160 thermostat and then aftermarket aluminium radiator with twin thermo fans. I run a 160 because on the Dyno my car makes 50 horsepower more at 160 that it doesn't 190. But I can't get it to run at 160 as it pretty much always runs around 190 to 210.
I'm now looking at the radiator capacity as these are a truck motor. Can anyone tell me what a Dodge Ram radiator capacity is?
I have cut the middle of the thermostat out and taken it for a drive. It does seem to be a little bit more consistent around 190 now but this was on a cooler night run.
Wishing for anything under 190 with the 5.9 Magnum engine is this unrealistic.