I know this is going to seem silly to you but what you have is the V-8 from the factory. The Part your looking for is called the Upper Baffle Extension.
There is also a Lower filler panel extension and a lower baffle brace. I don't think they reproduce any of them.
Most trucks were 6 cylinders and the radiator mounted to the cross member. On the V-8's they used the extension panels to move the radiator closer to the engine.
Unless your building a numbers matching correct restoration you don't have to set the rad back and you can use a crossflow rad and electric fan or a fan shroud and a clutch fan.
On my build I'm using a 5.3 L V-8 and a 2000 Camaro Rad and fan assembly. (see pic's I'm using as a guide for my build)