I have been reading through this thread a couple of times, one thing that interests me, from the Milne Report, to scrap the 800 500s and 400s and build 50 mixed traffic locomotives. This really was a bit surprising, considering the 800s were only a few years old along with the 400s having only been rebuilt, both had massive investment from the rail companies and also the reliability of the 500s to simply scrap them after so much money being poured in seems a bit pointless. And 50? There was already a surplus of reasonably modern mixed traffic engines, the woolwiches, the j15a's and B's also the more modern D's and the cattle engines
It had already become clear that rail traffic was decreasing by the 1930s so I can't really see how 50 locomotives could be justified. 20-30 at the most, but then you would also have the problem of the glanmire road tunnel, which double or even triple heading was sometimes required. This was one of the reasons the 800s were built by being able to climb it unassisted.