Rodger,
If you take some time and go back through the archives of RYPN, there have been numerous discussions about how feasible it would be to construct new large steam locomotives here in the US similar to the Tornado 4-6-2 project in the UK. The techonology that goes into just about every phase of building a steam locomotive still exists in the US today:
1. The Texas State RR has had more than one new boiler constructed for a couple of their steamers so the boilers are not problem.
2. Foundry technologies are still there as railroad wheels are cast all the time today. New spoked drive wheel centers have been cast for, I believe, Altoona's K4 and possibly a couple other restored steamers with cracked drive wheels.
3. The cylinders would seem to be the most complex challenge, but again, Strasburg has been working with the Austin Steam Train Assoc. to cast a new half-cylinder for the embattled SP 2-8-2 No.786 in Austin, TX.
4. The main frames could be made from two cast frames with cast frame spreaders just like many 1.5" scale live steam locomotives are built with today.
It all comes down to securing the funds, locating and lining up the qualified vendors and of course, having a thorough, detailed plan of how to "git 'er done" which I am quite confident that the SVRR boys are capable of. They, and the WW&F 2-foot group in Maine, simply astound me as they are proof that when you come together as a group around a single goal you can accomplish anything. These two groups are competely recreating completely abandoned railroads with correct locomotives and rolling stock all running on original grades. Now if only we could recreate David Moffat's Hell Hill Route over Corona Pass and the Moffat Tunnel. It would be a short operating season but would offer probably the most spectacular high-elevation scenery in the lower 48!