For years the standard solution has been Kadee's, kudos to you for thinking out of the box!! However, I want to add that there are differences in geometry among postwar Lionel, MPC, modern era, K-Line, Weaver, and MTH couplers. As an operations modeler, @Bob (Pennwest) explored a lot of this and wrote about it a while back. He spent hours tuning his couplers. I suspect the mfr's don't do it because of the time and labor involved.
Bottom line- if the geometry of the mating couplers doesn't complement each other in a certain way, they won't close together no matter how much force you apply. So if you're determined to do this type of operation, I would find ONE brand of rolling stock or trucks that works well, and stick with it. (If you're willing to cannibalize, you can always install one brand's truck on another brand of car.)
Thank you for sharing what could become a very valuable addition to operations-oriented layouts.
