Gary, the MTH smoke unit is not quite as long as the TAS or Lionel rectangular smoke unit, so it fits in front of the motor with about 3/16" to spare. It's tight getting the plate and screws in there, but with a little grinding, you can do it.
For the one I show, there was a big chunk of casting in the boiler that I had to totally grind out, there were a lot of diecast metal chips flying around!