Many thanks chaps.
I have got a bit more info from Dave Piggot at the RRHT. As far as the contradiction is concerned, that can just be down to the fact that different aspects of these manuals were compiled by different staff, and there is nothing to say that any of it should be taken as gospel!

Clearly the crankshaft torsional vibrations were never an issue in service, and these figures were printed early on when there was less operational experience.
Rather than using crankshaft dampers as were fitted to the Allison V-1710, Rolls-Royce instead tuned the front and rear quill drive and spring drive shafts to orders of 1.5 and 2.5 away from the crank frequency, and it was difficult to get the 1.5 order far below 1200 rpm.

Still, an interesting subject for total engine anoraks such as myself, and I would agree that the type of propeller fitted would no doubt have a bearing on how the engine behaves as there is a massive difference in the inertia of a Watts two-blader and a Ham. Standard 23EX as fitted to Lancs, weighing in at about 300lb.

Pete