That is correct. The GWR refused to lend the LMS a set of Castle drawings, but Maunsell was far more cooperative and lent a set of Lord Nelson drawings which were passed to the North British who proceeded to design the Royal Scots. Not being constrained by Midland practices, the NB designed locos with well sized bearings and long travel valves. As far as I know, The Royal Scots worked well "out of the box" - as you might have expected from a steam loco from the NB (the less said about their later diesels the best...).
Hmmmm. I don't think all of it is correct.
AIUI, the LMS was impressed with the Castle and did want to buy a batch from the GWR (50 sounds about right), but they were stopped by the government (would that have been the Board of Trade?) because it was deemed unfair to the private manufacturers. (I'm not sure why, possibly because of fears of cross or hidden subsidies.)
I'm neutral on the 'lending drawings' question, ie I don't know.
However, on the story of the SR lending drawings to North British, I believe evidence shows this is a myth - poppycock, even.
About 15-20 years ago, on the then LMS e-group, this story was discussed. In the group was an older gent who had worked as an apprentice in the North British drawing office. He was there when closure came, and knowing history was being lost, or threatened with such, he went through the drawing office files, and found hundreds of blueprints, all carefully numbered and recorded. I think he actually mentioned some interesting classes/designs, which I've forgotten.
But of Lord Nelsons there was no drawings, nor trace of such, ie no missing numbers around the time that any drawings that might have come, been recorded, but subsequently been lost.
He concluded there were none, and never had been. My thesis is that in the mid-1920s, it would have been normal around the bar room table (or platform trolley if under 18) for folks to talk about the similarity, at least externally, of the LN and parallel-boilered Scots, and this is how the tale began.
OF course, they looked quite similar, they were both designed to do similar jobs within the same loading gauge - but equally, in the guts, they were about as different as you could get - the LN was four-cylinder, the Scot was three, although they both had Walschaerts gear, of course. But if the whole point (as the myth goes) was for the LMW to 'big-up' its locomotive fleet ASAP, why go to the bother of redesigning the cylinder arrangement, and all the valve gear and associate gubbins?
My conclusion is on the lines of the NB draughtsman, largely based on his research. It is simply false.
I think that an improved 4700 Class 2-8-0 with 5' 8" driving wheels might have been best for the Devon banks. You tend to get better adhesion with 4 rather than 3 driving axles. And it could have eliminated the need for much of the double-heading.
Now that sounds a highly cost-efficient solution: no more outlays on separate designs, more parts, just knock up another what, 15 x 47xx?
What improvements were needed? I thought the 47xx were supposedly good machines, bar their RA?
.... It did mean that Mr Churchward's legacy powered half the railways of Britain, until Riddles ruined it all. There, that's been said. Stand by for incoming missiles.
You need to be better informed about the latest high-tech methods.
Put it this way, it's been said that former paint shop experts at Derby have been spotted in a garage wearing special, all encompassing suits and breathing apparatus, and that one had died an horrible death after an accident working with some new chemicals.
I'd wipe your outside door handles three times a day and carefully burn the tissue afterwards if I were you.