Lionel knuckle couplers

The different looking coupler is known as a Scout coupler since it came only on some of the early postwar Scout sets. It will not mate with the regular knuckle coupler, but Lionel made adapter plates with a knuckle coupler that could be clipped onto the axles.

In fact, any coupler plate from a 50s era freight car with metal trucks could be used. Just bend the tabs carefully to remove it and then rebend them on the scout car. You don't have to remove the scout coupler - just turn the truck around so that the scout coupler faces inward,

Some plastic knuckle couplers were non-operating, solid, one piece castings. You might have some of those on the older Lionel cars.

Jim