For those of you not familiar with it:
As a wargamer, whenever I see an episode one of my first thoughts is, "Wow, they have some great terrain!" So sometimes when watching I'll idly imagine a battle across the sets. Sodor invaded by Chaos Marines, Tyranids, Orks, etc.
But who would defend Sodor? The Imperial Guard of course! Thus was born the Sodor First and Useful.
With such advanced machine spirits in their vehicles, Sodor certainly uses the same technology in their tanks. After all, Thomas *is* a tank engine! So here's a preliminary shot of the Sodor First and Useful:
(image defiled with permission from Freddie Yu's Galen Rockhounds)
Building the Army:
Of course tanks are going to be key. Get as many Russes, Chimeras etc. in as you can and put the faces on them. Different paint schemes to represent the different engines from the series is a plus. The drivers in the series wear blue uniforms, so this would probably carry over to the IG as well. Since he's already a bit big it should be possible to turn a Creed figure into Sir Topham Hat/The Fat Controller.
++To die for the Emperor is to be Really Useful++
(you can see more of Freddie Yu's excellent Galen Rockhounds on Dakka Dakka)
(update - more Thomas related 40K madness over at The Back 40K)