I lived with the Sergent couplers on these cars for a while, but found them very frustrating to use. So, I switched these cars back to the Walthers ProtoMax HO-scale couplers. As with the previous conversion, I needed to do some custom work to make them fit. After assembly, I glued the couplers to the body using superglue. In normal use, superglue will be sufficient, but since there is no mechanical fastener used, a hard hit could knock them loose.
I also discovered that the couplers sat too low. To fix that I installed these washers using superglue, which were a perfect match.
Here are the three cars converted to the ProtoMax coupler. While not as nice-looking as the Sergent couplers, they are much more fun to use in operating sessions.