Which brings me to the replication concept: if three identical 2-8-0's can be fabricated using wheel centers, cylinder saddles, and boilers which can be mass produced (as well as myriad small parts) and applied to 4-6-0s, 2-6-2s as well, just by varying the frames and running gear, stretched to standard gauge or reduced to 3 foot, might it not be also more cost effective in the long run, especially when the lesser operating maintenance cost of using modern stuff like force feed lubrication and roller bearings is taken in to consideration?

This same subject came up in another publication in recent years. IMHO it is impractical from a cost standpoint to consider such replication in the USA. The funding is not there. Tourist operations run on tight budgets with meager if any support from dependable outside sources--read: government. The UK has their Heritage Lottery that can and does fund such work there, if only because the rail hobby is so pervasive and revered as to enjoy wide support. I think it a fair bet there are 10 times as many serious railfans per capita in the UK vs. here. As for any modern USA steam locos (e.g., NYC 4-6-4) those were all built on one piece cast frames, the production of which would be prohibitively expensive now--if it could be done at all. UK locos used plate frames, easily and relatively inexpensively produced from big pieces of rolled plate and programmed cutting torches.

MNGRR is doing a lot of replication, including covered bridges.

Minor point of order:
They did not "replicate" a covered bridge. They offered a place to go for an authentic wooden "covered bridge" (technically a boxed pony truss) that had been removed, disassembled, and restored (with some new parts) at a university campus at another location.