Gentlemen...
Having "been there, and done that", a locomotive restoration, I want to mention some things, provoked by the recent postings, that come to mind. (For those who don't know me, I brought Baldwin boiler #58686, a little 2-4-2, in from Hawaii in 1965, and restored it to operating condition.)
First, there were many times when I thought it would have been easier to start from scratch. A good example is the rocker links in the valve gear. The corrosion, from the Hawaiian weather, had pitted them terribly. I ended up just ignoring it. I cleaned them up, polished them. There was so much over-design in the original, that there was no need to have perfect surfaces. And, it has all worked out fine. Perhaps the pits just hold the lubricants.
A new boiler for #5 cost me some $6,000. A new boiler for a big locomotive, such as a K-36, would be much more. But, if shopped carefully, not incredibly expensive. Boilers are built every day. They, of course, are welded. But, that doesn's show. I'll bet you I could get a K-36 boiler for $100,000.
I was fascinated by the locomotives at Promontory, when I visited there some time around 1975. I walked down to the staging area, and said to the engineer, "This doesn't sound like a wood burner", and invited myself up into the cab. He admitted they were running on propane, and invited me to go on the next day's trip down from the engine house. (Unfortunately for me, I didn't want to delay my drive to Chama.)
Well, there are some relatively large steam locomotive being built today, in China, and for zoo railroads. There is nothing incredibly expensive about them. After all, the technology has been around for a long time, and is still in wide use.
Well, I've not posted all my thoughts on this subject. As I work on the design of a new passenger car for the C&TS RR, I have in the back of my mind a fleet of new C-16's working out of Chama.
Cheers, Bob Keller