> What were are the failures of the original design???

If you feel that Wikipedia is a reliable source, its article talks about the two biggest issues, which were excessive wheel slip from the locomotives being so powerful (too powerful perhaps) and frequent failures of the poppet valves.

[en.wikipedia.org]

The article also mentions the incredible maintenance costs of the locomotives. Cost of ongoing and FRA 15 year maintenance is something that nearly every steam locomotive group deals and even struggles with, but this T1 locomotive the maintenance issue would be even more so. It would be very foolish to build one with NO plan on how to continue to maintain it in running condition. As I said before, a VERY expensive new from the ground up static display.