We have used Dewalt transmissions for several years based on the " Nothing But Dewalts" white paper. The best way I have found to do it is to get the exact parts from
www.dewaltservicenet.com. If you search for DC980 you should find all the parts referenced in that document.They have been obsoleted but still may exist.
The drills you referenced aren't the same design and probably will require a different conversion process. I'm sure it can be done but I have no reference.