Why 42? A couple of reasons, somewhat inter-related...
In doing these paint schemes on the computer, the letters and numbers are done pixel-by-pixel; very painstaking. It had to be in the low 40 series, and 42 just looked good.
Also, more information had come to light. I knew the 10 class 4-8-2's had been renumbered (on paper) to the 40 class when the RS-3's came; I assumed the numbers started at 40 (40, 41, 42), leaving 43 as the next available number.
Jim Boyd, in researching his L&HR book, found that the 4-8-2's were actually renumbered as 43, 44, and 45- this from the records (never did ask him if he found out why those numbers).
It's a 'work in progress'. Haven't finished playing with a herald (yes? no? version? placement?). Large painted number at the rear somewhere? Four stripes? wider stripes?
For now, it stays the way it is. And, thanks all for the kind comments.