I read that article and can not find what bore the BB heads were tested on but I bet it was the bigger 440 bore so on a 383 they will probably flow less wit the smaller bore and since they are almost tied with the magnum on the intake already they will probably flow less on a 383 than a magnum will on a 360 plus you lose the efficiency and no leak sealing of the magnum design. Also the 300 hp crate motor might make 320+ hp but remember the M1 single plane can not hold the jock strap of an RPM air gap AND the truck cam is actually bigger and better than a 300hp crate cam. I bet if you gave both of them the RPM intake and a set of headers the 5.9 magnum would make for a faster car with a broader TQ curve with less leaks and more MPG and weighing significantly less without buying expensive aluminum stuff.