Dr. Evil’s - er Victor’s ideas are indeed inspriational or dilusional, not sure. The cab should come off fairly easy with tabs and a couple screws. Don’t worry if you break them, you’ll do worse. Make a new floor from some 0.60 styrene or plexiglass (even wood or metal) and screw it to the existing. You can hide the screws with an oil can or seat later.
The trailing truck can come from a scrap bin or cheap model. Use some sheet brass or styrene to make a bracket that will be attached to the underside of your existing model with a screw, washer and a small spring to allow some up and down movement.
Think about an enclosed cab - cool stuff! Then you won’t have to worry about screws showing. : -)
Neil
P.S. While you’re at it why not look at making it more to a scale. There are too many to bring up but choosing one now and sticking to it will save you headaches later. The diference between 1:24 and 1:20.3 are huge! Even 1:22.5 or 7/8" (2’ gauge) but a standard for heights, widths, and coupler heights will be much easier.