Its generally best to run the oil through the radiator cooler first and add an additional cooler in series after the radiator cooler if needed. If you're running a 318 with slightly over stock stall (does "300 stall" mean 300 over stock?) I wouldn't think you would need an auxiliary cooler.

A little more information about your combo would help (engine, trans, convertor, rear gear, how you'll use it).