[Steeveedee]

You will need a good radiator. Look at what is put in a vehicle of the era that the 400 SBC for the amount of area you need. A '67-72 radiator will give you the idea. Your truck has a down flow radiator, so I'd recommend at least a 3-row if you don't have AC. Chevrolet cheaped out in '71 and put 2-row radiators in big wagons with AC and ate a bunch of engines under warranty from overheating. It wasn't the engine, it was the piddly radiators.