Remove the roof by cutting from the inside of the body. This will leave thin rivet strips on the sides that can be carefully cut off. Keep them as they come handy for covering an problem zones created while splicing together the sides. Then, again from the inside, cut out both ends. I used a doors and one end window for each side from the ends for re-usage on the sides and discarded the rest.
Sides Now create two symmetrical side parts by cutting and slicing the sides of the caboose.
These side parts determine the overall length of your model, so make sure your drive fits underneath. Good planing pays in this step. The doors should go into one end on each side so that your personnel can access the cab easily. Fill in all rivet lines destroyed during this process with bits and pieces of the strips from the first step. Front This part determines the width of your finished model.