Go argue with the Chrysler engineers. This was their information in the day. Slower in the block allows more heat transfer to the coolant and then more reat transfered to the air in the radiator. Your results may differ, but the old Chrysler engineers were pretty fart smellers.
Since posting previously, I have seen the photos of the fan and shroud. The fan is pulling air partly from the engine compartment and thus loosing draw through the radiator. The fan could be spaced ahead, but you do not want to get too close to the core. More work is involved, but a better solution is to space the shroud back. It would also be advantageous to roll the inside diameter about 45° on a 1/2" radius, in the direction of flow.