Honestly, it's really not rocket science with this stuff guys. I splice frames in a hotel room with my little jewelers saw as I do 95% of my modeling in a hotel room while doing real railroad stuff. It's just a matter of cutting straight and splicing.
I chose to try grafting on a resin casting of the forward drive box and cylinders in front of the original 1st driver. ill go get some pictures of a chassis in the morning.
All i can say is practice, practice, practice. You can spend months here talking about doing this, casting that, or 3d printing the whole damned thing but in the end, you can build one of these a night once you get the process down.
Drasko