Cooling a clone.

I feel your pain brother. I have a supercharged 340 in my '69 Dart and it's always been hard to cool. My setup is this. I have a Champion 26" aluminum cross flow radiator with a 7 blade steel factory fan with shroud. Additionally I have an electric pusher fan on the front of the radiator along with a separate tranny/engine oil cooler and a Brass Works high flow water pump.
I still couldn't idle in traffic for long periods but when moving it rarely went above 180*.

I have new hope though, since I installed the new Fitech EFI it appears to be running cooler, we will see. Good Luck