the mounting post for the couplers on the thomas line are lower than the height of regular ho cars. what you would need to do is convert one of the thomas trucks by mounting a coupler that works with your other cars on one end of the thomas car. to do this you would have to cut part of the mounting post on one end so that the coupler is at the correct height. use a sharp knife or saw and a file to smooth the cut post, then screw the standard (or kadee coupler if you use kadee's) in place.
This kind of car did actualy exist, but it wasn't used to link up thomas and friends to normal american cars in real life. It really was used to allow standard gauge engines to move around narrow gauge cars and vice versa.
Just thought you'd like to know
