I built a steam coach, using a Marx chassis, and l thought of doing an inspection engine, as very similar in construction. Except maybe a Marx "Civil War" chassis might work, as they are often found with plastic cabs and bodies (severely) damaged. I will bet somebody has done one, although l haven't seen another steam coach posted, either. Have seen some interesting inspection locos pictured, some with steps and seats up from the pilot. Different is good.