This conversion is from Kadee after I sent them an e-mail asking about how to do this conversion. The recommended coupler is a #789 for the "G" scale coupler and the #1789 for the "#1" scale coupler. This conversion will provide closer coupling than the original Aristo coupler, and will still allow the Dash 9 to negotiate 8 foot diameter curves pulling 40 foot or shorter cars. The delayed action will still work even with cars that have truck mounted couplers. With curves of 10 foot diameter or larger, cars longer than 40 foot can be run with no operational problems in either the coupled or delayed position.
The first step in this conversion is to remove the original coupler from the pedestal while retaining the original screw and washer. Remove or cut off the wire centering spring. For removal the screw for this is rather difficult to access, but a long Phillips (1x4 from Sears) will do the job. Trim off the side walls or ridges of the shank of the #789 draft gear box. Drill a 1/4" hole through the smaller hole in the shank. Assemble the coupler and slip it over the pedestal so it rests on the ribs. Set a washer of 1/4" interior diameter over the pedestal onto the coupler box shank. Secure with the original screw and washer. Tighten the screw enough so the assembly is firmly in place. The coupler opening will keep it from pivoting.
Place the locomotive on a spare piece of track and check the coupler height with either a Kadee Coupler Height Gauge or use another car with a properly mounted Kadee coupler. Make sure that the coupler is level. If it is too low, check to make sure it is sitting on the ribs of the pedestal properly. To tilt the coupler up, you can place a very thin shim under the rear of the shank so it sits on the rib.