As far as cooling, I am on the side that says to use the same arrangement the factory used in these earlier cars and trucks. I like a mechanical fan system and will not use an electric system on anything I build.
I'm certain there are components that are available out there to make up a whiz-bang electric fan system. I'm just not interested in messin' with 'em. Now, for you guys who are gonna make noise about less hp used to cool the motor, the power to operate the fan is made by the alternator and the alternator is operated off the crank, so don't try to tell me that there is less power used with an electric system. It takes the same or even more hp off the crank to operate the electrical system because of the efficiency loss. Fellows, there is no free lunch.
Sorry Father and Son, had to get that off my chest.
Now, starting from scratch, we need a radiator that has sufficient square inch area to transfer the heat generated by the motor to the atmosphere. I would be thinking something around 375-400 square inches and 2 or 3 cores thick. I'd go to the boneyard with a tape measure and look at all the radiators that are in front of a small block Chevy. Measure them up, take pics, whatever. When you find one that will fit into your core support, write down the year, make and model, so that you can order a new radiator from your favorite supplier.
I bought a new 2-core aluminum/plastic radiator from Checker Auto for my daily driver pickup truck. It was $120. I don't care if it doesn't last as long as a copper/brass unit, it was only $120. And it cools the motor on the 4th of July in stalled traffic in downtown Phoenix, Arizona.
You'll need to direct the airflow into the radiator from the front of the truck. Look to see if there is a way, for instance, for the air to ride up and over the radiator because of the space between the top of the radiator and the underside of the hood. If it can get through there, you need to install baffles that will direct the air through the radiator, not around it. Check the side and bottom of the radiator to make sure air cannot get around the radiator.
Now, we have cooling air coming through the radiator and we have a good radiator mounted. The next thing is the shroud. We want a tight-fitting shroud so that the fan cannot pull air from around the sides, top or bottom of the radiator. All air that enters the engine compartment must be pulled through the core of the radiator. I like to use OEM parts because the manufacturers spent untold amounts of money to engineer the stuff to work properly. So, I use a steel, 18", 7-blade fan. Grab one from the boneyard. Lay it down flat and measure the pitch of the blades from the floor to the edge of the blade. A good fan blade will be about 2 1/4 to 2 1/2 inches pitch. Some of the diesel Olds motors from the '80's have a 3-inch pitch. Don't you just know that they hauled in some air.
The blades should fit into the shroud hole with about 1 inch of clearance all around the hole and with the blades sitting halfway in and halfway out of the hole or maybe just a tad deeper into the hole, say 2/3 in and 1/3 out. The fan will be driving off the water pump. Before installing the new water pump, hold the housing in one hand and twist the impeller with your other hand. The impeller must not move. That's another hard overheating problem to find, the impeller slipping on the driveshaft. Check for a little clearance between the housing and the impeller and between the impeller and the rear plate. If there is any touching going on there, you will have a noise that is hard to find. Also, make the proper clearance between the water pump plate and the timing cover. Also, use the proper diameter pulleys so you get the proper fan speed. Oh, and use a thermostatically-controlled fan clutch on the pump shaft.
Be aware that there are serpentine systems out there that turn the fan blade counter-clockwise, so don't be fooled by this. As you are holding the fan blade in front of you and looking down on the top edge of the blade, if the blade has a Northwest/Southeast orientation, it is a conventional Vee-belt fan blade. If the blade has a Northeast/Southwest orientation, it is a serpentine blade. You need to know this when scrounging through the boneyards for parts.
That's my best shot for a bulletproof cooling system, although there are some excellent tips and procedures written here.....