As per Terry's comment, Burt's book on 1919-1939 period will be useful. Lots of profiles of R class ships from those years, plus drawings of their bridgework from various angles.

I like the idea of converting Royal Oak to a late 1930s Ramillies but, from memory, there are differences in the bulges. Both ships had the very large bulges unlike other ships in the class but, if I remember correctly, those of Ramillies did not extend as far forward or aft as Royal Oak's. You might want to double-check that.

Chris