In the past, I have been very happy with Haydens 7 bladed 18" stainless steel blade flex fans. I ran one of my old 70 428 CJ Mach 1, it always maintained a good temperature, and I recently installed the same model fan on my 59s 428. I have also had good cooling with a 5 bladed Ford PU truck fan, kinda looks like a flex fan, but the blades ,which are riveted to the center, are so thick, that they can not flex. Cooled well, but quite noisy.