The stock model.
These photos show how I converted the standard Rapido coupler on the locomotive to the Micro-Trains 1015 ones. The Doodlebug has a linkage rod that connects the rear truck to the rear coupler so that it behaves like a truck-mounted coupler - it swings with the truck.
The coupler and the truck are each mounted to the frame with a screw. I had to cut the linkage rod in half to get the parts to come loose. The oval-shaped brass part that sits under the screw of the truck is needed to mount the truck back in place (otherwise there is nothing to hold the truck up).
Once the parts were removed, it was a trivial task to glue up the MT coupler with Walthers Goo.
Here is the final result, right side up.