That is some amazing re-engineering and fab work. The "heater hoses thru frame rail" setup should earn brownie points at a mod. car show, not that I would do it my car and risk rusting out the frame rails.
The aluminum radiator and shroud should be a great improvement. I got a new Be-Cool one on ebay for $80, but ended up putting on my Newport because it would have required cutting off the frame rail lips on the Dart to gain another 1" width, but would probably fit the wider 66+ A bodies.
I have heard the "water moves too fast thru radiator" theory before. It doesn't match anything I learned in engineering and 35 yrs design experience. Indeed, my M.S. theory was experiments in liquid heat transfer. Could be right for some esoteric reason, but more likely another example of how mysterious thermodynamics is to the un-schooled.