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Built with a lot of the same parts as two combined Toy Story engines, I'm aware that there are visually quite a lot of stylistic similarities. However, a closer look reveals that that's about where it ends as it's been entirely redesigned. (A big part of the reason I consider it a MOC and not a MOD or "kit bash".
The wheels on the front truck are a bit larger than I would have preferred, although the lack of tiny red wheels plus my choice of articulation ended up making me decide to stick with the red wheels.
The piston design is one that I've quickly grown attached to, after finding myself wondering one day if the 4L bars would fit into the bottoms of these cylinders. Turns out they fit perfectly, and taking that combined with track sprues and Tony Sava's awesome awesome idea to use the Minifig wrenches (As he did on his American engine). The result is a nice looking piston with almost no friction, and it's certainly one of the aspects I'm most proud of.
The problem of how to attach the dome and bell was another one of my big challenges, as I was set on a properly rounded boiler and didn't want holes or gaps in the boiler itself. Looking at my reference picture presented a solution however, and the handrails came to save the day. There is a minimal gap which is virtually invisible from any angle other than this one, but it keeps the boiler visually intact and gap-less. The smokestack went through several revisions, as did the headlamp, but in the end I found a satisfying solution to the smokestack and I decided that a slightly modified versionof the TST's headlamp felt suitable enough.
I removed a piston here to help highlight the method of articulation, which also went through a lot of revisions. It has more than enough swing to clear the pistons through any corners, and it's actually built so that the front truck is a plate lower than the rear wheels; which was deliberate for several reasons but mostly due to the engine's very low weight. In the end though, the engine runs very smoothly across any track combination and rolls so easily that any degree of incline sends it running off.
The tender is very simple, but I tried to make it similar to the reference picture as much as I could. To be honest I'm not sure what the slope-y bit in front of the tender's water tank is for, but it was in my reference picture and added some visual interest so I added and kept it around.
The part count for the engine overall is under 300 pieces, and it was first real foray into learning articulation. In the end though, I couldn't be more happy with how smoothly it rolls and I'm very pleased with a number of the building techniques. This year I'll be displaying my engines at the Phoenix Comicon with the CactusBrick LUG, this engine is the one I'm going to be running most of the display; though most of my engines will be there. From that I should be able to get some running videos.
That's all for today! My latest engine is holding on a very slow bricklink seller, but it should be posted soon.
Plenty of the building techniques were the result of "Eureka!" moments when I was pondering build problems at work. 
