Big engine requires big radiator and high flow fan. Because of limited size restrictions, you might want to give Champion Cooling Systems a call to see what they recommend. You can look them up on the net for their phone number. If you haven't already done so, check your thermostat. Run the engine without one and see if it still overheats. It's also might be possible that when the engine was built, the head gaskets were installed backwards restricting coolant flow. I do not know if this can even be a problem with your engine, but for some it is [my Ford 302].