I dont really see a need to re-desgin a draft gear box to hold the coupler though. The Kadee draft gear box is just fine. The engine coupler mount still needs the complete Kadee to slide in it. It's just a spacer with a decorative front for the pilot. If the Kadee is the proper height on the cars, and flush with the end sill.... what else do we need?
Mounting the Kadees at the proper height and location is the key... and the Atlas spacer provide just that.