Since there was some interest expressed in the Williams GP9 pilot thread here, I figured I would post some details of the design for the pilots I'm doing for my SD90. It's an old one and we've been through a lot together, lol, so it's also one of my favorites.
First, a few overall views of the design:
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 (0.040" mounting holes are provided for this). The various air hoses are separate parts, to facilitate painting and weathering. The cut lever is part of the main part and is fixed. The main air hoses are modeled as though they are suspended below the couplers by a chain or lanyard. I figure a bit of thread or tiny chainlink will do here. 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, and is bonded directly to the engine chassis. This does a couple of things. Most importantly, it 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.
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. No guesswork. You can see the features on the pilot that facilitate this in the pic 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:
As far as applicability to other models, the exact model I have is this one: http://mthtrains.com/20-2370-1. It's a 2002 model, but I imagine the newer models probably use the same molds, etc., at least judging from a few of the pics I've looked at. Once the design is truly finalized, I will post detailed dimensions of the parts, so that folks can verify that it will fit their models. Who knows, it may fit other units as well!
So there it is. Comments, suggestions, ideas for tiny-but-cool details to add, whatever - have at it.