I remember changing the feed and return fittings on the 03+ transmission to get it to work with my 01 lines and cooler, like mentioned above. I browsed through it, but I believe you can't really get the checkballs wrong unless you do one-off parts. They changed the size of the fitting containing the checkball on the newer transmissions with the built in checkball. So the older fitting will not work on the newer and the newer won't work on the older fitting. I don't know about switching the actual lines over and the design differences or any benefit.