Here's a Kadee conversion that I did for my MTH Great Northern S2 (http://mthtrains.com/20-3499-1) that I thought folks might be interested in. This is a superbly detailed engine to begin with, so it's a nature for a Kadee install.
The original configuration:
For reference, here's what the real thing looks like:
The view from the underside of the tender (you can see the coupler mounting boss on the truck will need to come off to clear the Kadee gearbox...)
After a rather involved disassembly of the tender and dismantling of the truck, here we are at the point of no return:
Here is the 3d printed mount that I designed, bonded to the pilot:
There is a slot on the front of the mount (just visible above) that engages the sheet metal chassis when the pilot is in place, to help carry the load on the mount. The pilot and coupler can be removed as an assembly, in the event it is necessary to get inside the tender again. Here is what it looks like installed:
And with a car behind it!
The disassembly and prep on the tender was a little time consuming, and requires a bit of fortitude when it comes to the hacksaw part 
, but the end result is worth it.
If anyone has this engine and wants to convert it, let me know and I'll set up a Shapeways page for the mount.
Eric
