Why is it on some radiator fans the blades are symmetrically spaced and some are not. In the process of purchasing fan for my 340 but am reluctant due to the blade orientation. It's a 340 fan with 2 1/4 pitch part number 2863 215. My research indicates this is for a 340, Mine is a 70 model engine going into a 68 Barracuda. Any help would be appreciated.