You beat me to it Mr G!
Given that the restoration took ten years and cost well in excess of £4 million ($5.6m+) you can only speculate as to how much of the original engine is left.
I think that they must go by the principle that if the name plate is original, then it doesn't matter what else you weld, bolt, rivet or otherwise attach to it.
I mustn't be churlish; it's great to see it under steam again.