If I am stating the obvious I apologize but figured I better mention it. If you look at Dave’s car each of the paired trucks (two front and two rear) are attached to a “bolster” of some sort (in Dave’s case basically mini flat cars) that the car then attaches to. This is the only way to get all four trucks to track other wise they would bind on anything but the largest of curves. By doing this it will take much much tighter curves. And the closer those pairs of trucks are to one another the tighter the curves are even more. I am tackling a similiar project with a 16 wheel four truck heavy flat car.
If it were me I would first design each pair of trucks and then take like you said and use a piece of wood or cardboard and mount them and see what it looks like. Another thing to keep in mind is even if the car is long but will physically roll through your curves, if the trucks are a long ways apart it will have some considerable inside over hang and may hit stuff staged close to the track on inside curves.
Neat idea but there are some considerations.