I always like to hear about enthusiasm like this, and we can only hope they have the money and time to restore these. Given that UP was basically going to scrap them, or maybe give them to someplace to display them statically, this to me is a good thing. I suspect they will run the challenger as oil fired, not an expert on steam but quite honestly building an oil fired tender shouldn't be that big a deal, it is an oil tank in a box *shrug*..seems to me it would be more time consuming to rebuild the engine to run on coal again. Coal has the fire problem, plus the other thing is that as expensive as oil can be, coal is expensive and with coal mining in decline as power plants convert, it may be harder and harder to get coal to boot.
The analogy to the FRA rules is airplane regulations, FAA regulations require there are time intervals for inspections (I don't remember the intervals/levels, in the UK they call then Class A , Class B and Class C). At those intervals certain inspections happen and certain parts have to be swapped out for new or rebuilt ones (the ones swapped out get tested and if needed, rebuilt, to be used again). The second level requires more, then the third level, After a certain length of time the plane basically is almost torn apart and inspected stem to stern, they look at the airframe and the structural members, pressure test the fuel tanks, you name it...and that sounds a lot like the FRA 15 year inspection looking at the form (albeit in a different way).
I am sure it is a challenge, given that they pirated it for parts for 4014, and it hasn't been run in a while, but it doesn't sound like something that with money and time they can't do. I am sure it will be costly and require finding ways to scrounge up parts that can be rebuilt or made from scratch, but if the guy has the donors, it sounds great.
And if they fail, the engines will be no worse off than they would with the UP, where they likely would have ended up scrapped or maybe given to someplace for static display *shrug*. One thing I will note, it sounds like the UP team would rather these engines have a home where it can run, they could have easily scrapped them or given them away to a museum that would put them on static display. I can understand why they had to get rid of them, I am sure the beancounters were harping on them about having stuff in inventory "not doing anything".
