I think I may have a simply solution. I took apart my MTH SW9 Cow and Calf. Looking at the guts, it dawned on me all I need to do it buy another MTH SW9 cow any road name at all, ditch the shell, and put the calf shell on it, then make a lash up! Smoke unit not solved but I can save that for another day. The Cab section is hollow and there are not parts that occupy that space so, the calf shell fist no problem!
Now to just by another SW9 in a road name I don't care about.