Ok, so finally getting back to this one after a long delay, here is the design for the ES44AC pilot and coupler mount set. The specific model I am working with is http://mthtrains.com/20-20285-1.
From the front:
From the rear:
The blue and gray parts are models of the existing chassis and body shell. Everything else is part of the new assembly. The pilot is intended to be bonded to the body shell, so that the joint can be made seamless, and so that full length handrails can be permanently attached to it (0.020" mounting holes are provided for this). The various air hoses and the front plow are separate parts, to facilitate painting and weathering. The cut lever is part of the main part and is fixed. The MU cable and junction box for the front is a separate part that can be added if desired.
Here is a view of the assembled unit from the underside:
The coupler mount is a separate part from the pilot. This approach provides a way to disassemble the engine without having to make any changes to the original parts. It also provides a good load path from the coupler to the chassis - the pilot, plow, and body shell are purely cosmetic and carry no load. The engine can even be run, tested, etc. without the body shell installed, but with the couplers in place. Although the coupler mount is designed to be bonded to the engine chassis, I have also provided locating holes for screws in the event a less permanent installation is desired. For this engine, the coupler mounting tab on the truck may need to be removed to provide clearance to the back of the Kadee housing - I'll update with details after I get the parts installed.
The pilots are intended to be bonded to the body shell first, and then serve to locate the coupler mounts on the chassis during their bonding to ensure reliable alignment of everything, as shown below:
Here is what the body shell looks like fully assembled and removed from the engine:
And here is how it comes apart for maintenance, once everything is installed:
So there it is. As before, comments, suggestions, ideas for tiny-but-cool details to add, whatever - let me know. 
I'll get a Shapeways page set up for it once any final changes are incorporated.
Eric
