I had a 512" RB in a Duster a while back, Indy top end, pretty stout cam - PO had aluminum radiator, electric fan in front, no shroud, mech fan.
Ran 200-210, would go up on a hot day in traffic.
I ditched the electric fan, added a shroud, and swapped in a smaller water pump pulley.
After that, 170-180 no matter what.
Radiator was a 26" in the 22" opening.
ATF cooler was separate from radiator.