I'm not much into foreign trains, but even the most Brit-centric enthusiast can't deny the USA "Big Boy" steam engine returning to steam is an incredible thing.
While not brilliantly filmed (get a tripod!) this video shows an early run where it is paired with a 4-8-4 and just be on the safe side, some sort of diesel. I'd very much have enjoyed seeing this one!
Also, aren't US Railfans well behaved compared to the muppets watching Flying Scotsman in the UK? Do this in the UK and you've got people standing on the ballast having decided that fences don't apply to them when there is the chance of another photo of the most photographed locomotive in the world at stake.