Well.. what's all the rumor about the "Mallard"?
How fast did it really go and how long can it hold this speed?
I don't believe in the 125 mph - I think the "Mallard" did it once, but never really again. Because there are reports, that after this run the middle drive rod had fractions, two of the main bearings had failures and the bearing temperature were close to the red flag.
So it outbet 05 002 of the german Reichsbahn, but 05 002 was able to go the 200 km/h a couple of times without damage - but it wasn't able to keep the speed a prolongued time, because it was tricked by using the so called "boiler capacity reserve" - on which a firemen established hell in the firebox. A good burned fire is densely packed and maintained, then the boiler is feed up to the highest possible top and then the fire is made hell. Now, with the heat of tousand devils in the firebox, the boiler steams, usually more than the feedpump can deliever, thus the water level drops on those high steam consumption rates - but you can overpower the engine, thus reach top speeds. The track of 05 002 on record run was even, those of "Mallard" slightly descending. So "Mallard" was running downhills, 05 002 was running on even track.
"Mallard" failed after the record run and needed service, 05 002 was only low on water and needed shut of the throttle and waiting till the feed pump raised the water level again... after this, the process could have repeated - for another sprint of 200 km/h. Thus 05 002 was the secret winner of this, but german not only lost the record, but also a war and this development was stopped.
Thus regarding the power of the T-1 the "Mallard" is no match, even 05 002 is no match for the most US locomotives. Even the ALCO series 800 is much stronger and better designed as the 05 002, thus outbeat 05 002 in power and speed duration, if you want to try.
US locomotives travel usually only around 80 up to 90 mph, but the loads they carry would overload the british A4 series at start, and even outbeat series 05 of germany with ease... thus don't compare those runners with each other...
To rebuild the T-1: Well, this is such a big project, I think this won't get real.
Allways keep two-thrid level in gauge and a well set fire, that's how the engineer likes a fireman