Sadly I suspect that book will be taking the as used and modifed version with the valve gear bodged (they were classed as lower output due to this).
The valve setup was very advanced on these, way ahead of its time but, the actuator cables had to sit in a bath of oil and exit through rubber seals. As you can imagine, the seals wore very quickly due to the soot, grime and dust associated with steam locos resulting in the oil being dumped an the gear seizing up hence why they get modified to a more standard setup.
Will be interesting to see what it does in its as designed setup because the original trials should muc grater output than the mainline listings for full service had! 
Indeed, and they often caught alight, along with the chain drive slipping and causing the valve gear to go out of synch. with the pistons (just as on a car) causing the engine to falter or to come completely to a stand.
As you rightly state the rebuilds, the first of which was Merchant Navy 35018 "British India Line" in February 1956, followed by the West Country's and Battle of Britain Classes, included the installation of three sets of Walschaerts valve gear for it's three cylinders. Along with multi-jet chimneys, outside blast pipes, new superheaters, and other advances in steam locomotive technology, these rebuilds were a great adance on the original "Spam Cans". As Martin correctly states the MN were rated at 8P, whilst the WC / BB were 7P5F even though their boiler pressures had been reduced from 280 psi to 250 psi, and these British Railways developed engines, although "light footed" were wonderful locomotives and are still valued by steam preservationist and their crews today. Indeed they are good "free steamers" and providing you, as a firewoman/man, keep the back corners of the grate well filled, but with a 'little and often' technique (true of many engines), and a good covering over the rest of the grate, they will provide enough steam for whatever the drivers needs.
Unfortunately all this development, along with associated ones, came too late to save railway steam locomotive traction, and further development of these great machines came to an end, with 9F 92220 "Evening Star" the last British built standard railway engine, constructed for British Railways, emerging from Swindon (ex-GWR) Works in March 1960.
..........until now with Peppercorn 'A1' 60163 "Tornado"!!
8-)
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Topic: Spotted an unusual sight today! (Read 1882 times)