Paul Tomlinson
Hi Nigel. To pick up on the points you raised, I’d agree that the best plan is to model a prototype for which you have a clear photograph – for LNER J69’s, for example, there’s a seemingly endless number of combinations of different buffers, chimneys, cab roofs, safety valves, wide and narrow tanks, wheel spokes…. Locomotives Illustrated no. 64 features, among others, the C2/C2X, Mike Morant has published a few of the C2/C2X online – https://mikemorant.smugmug.com/Trains-Railways-British-Isles/SR-and-BRS/LBSCR-tender-locomotives/LBSCR-C2X
I believe that the “X” in C2X denotes a larger diameter boiler – https://en.wikipedia.org/wiki/LB%26SCR_C2_class
Alan Gibson uses 1/8″ as standard for loco axles – though he does do other diameters in his “conversion” sets, to match whatever the RTR manufacturer used. Must be a bit of a nightmare for him… I’m pretty sure he uses 2mm for bogie and tender wheels.
I too like CSB as a means of suspension.
All the best.