It was only discovered that it was FR No 20 and not FR No 18 when the frames where sand blasted during its restoration and the Sharp Stewart works...
The tender engine is actually a 4-6-2 No 666 and not a 4-6-0 - it's a CC class loco as shown on the link below of one of is sisters . . ....
Sadly with such sweeping statements of the kind "she’s the only ya de da . . . " its easy to disprove such - try this page for starters (a barclay...
I would have thought the book by Phillipson would be a good place to start although its a long long time since I've looked at my original copy...
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