The engine is unaltered, its front coupler attached to a dummy coupler on the plow.
The plow is printed in two parts and snapped together. Guides at the bottom of the plow align the plow with the center rail.
I had to remove the rear guides for the postwar (623) engine. The 634 is a MPC.
As design software, I use SketchUp 2016 free desktop version.