66 Dart, 408 runs hot. HELP PLEASE!

You could run a 14inch electric fan or your fans you already have on the other side or the radiator and a flex fan cost around 25 to 30$ on the engine side that way at idle you will have I good air flow and the electric fans you have can kick in when needed and would also help cool off the motor when it's not running. When you run long tube headers it get like 15 to 20 degrees hotter under the hood. Would probably help with heat soak for sure running aluminum heads