[sassgrunt]

I know that you're NOT wanting to add a fifth wheel to it, but just as food for thought; that's what I did to mine. I never really liked the short (white plastic) stake bed, and did want the tractor to pull a semi-trailer. I bought a second white plastic bed and then joined the two to make one that's now 24" long. Used the frame from a Tamiya flatbed trailer, but cut shorter and with only one axle. Also used a Tamiya fifth wheel for the tractor.
It approximates a ZIS-120, more or less.