It’s very simple to convert Lima Mk3 coaches to use Kadee couplings. Just cut off the huge tension lock leaving a tongue of plastic and glue a Kadee number 20 coupling onto the top of this using Evostik Impact adhesive. Adjust the length of tongue and the positioning of the Kadee so that the coupling knuckle is correctly just proud of the corridor connection.
A similar approach can be used with Hornby (ex Lima) Mk3 coaches but the number 20 is glued into the existing pocket with its tail suitably shortened.
Once the glue sets this arrangement will easily take the load of a full length train being pushed or pulled and will navigate second radius curves.