K-Line provides an extra coupler for conversion to Lionel size couplers, however you may need some small screwdrivers to do the job with. I replaced the coupler on one of the hopper cars and put a Lionel bobber caboose at the end of the train.
Another possibility is to go with an Atlas Brand coupler or truck conversion kit for O gauge trains, you will have more parts than what you need leftover.
Lee F.