Let's talk about fixed-blade fans

What thickness core? You never said. I always have run the Mopar viscous fan on everything I have ever built Mopar and it has worked every single time. The 5 blade design is staggared and assemetrical resulting in more air being moved since each blade moves air at a different rate. That's how it is designed. It also requires the proper shroud. The correct positioning for the fan is half the blades should be inside the shroud and half out. The MP fan is a variable, thermostatic design that increases fan resistance as the temperature rises resulting in a fan that steadily increases in speed with temperature. Those things can really move some air. They are light years ahead of any fix blade fan ever made and work better than most electric fans. Also, you need to make sure as much air as possible is flowing through the radiator. Is the hood to radiator support seal in place? Are you running a valance panel? You can even add a bottom cover extending from the rear of the valance to the K frame blocking up those holes thereby forcing more air through the radiator, instead of up through the K frame. While you're at it, seal off ALL the holes in the radiator support except that which air flows through to get to the radiator. This forces even more air through that one big hole in the center. I use black foam pipe insulation. Works good and you cannot see it when done. Once you've gotten all that done, you should be well on the way to running much cooler.