It is very interesting that you are ROH’s Great-Grandson, and it will be great for your Great-Grandmother to see the frame built into a bike.
My 1950 ROH has 120mm rear dropout spacing, too. One can tell whether a vintage frame has been cold set from a narrower setting by putting a steel straight edge along the side of the chain stays. If this shows that the chain stays are slightly curved it is likely to have been cold set to a wider spacing at some stage. My frame doesn’t have any curve in the chain stays, and so mine was originally made with a 120mm spacing.
My 1950 ROH has 120mm rear dropout spacing, too. One can tell whether a vintage frame has been cold set from a narrower setting by putting a steel straight edge along the side of the chain stays. If this shows that the chain stays are slightly curved it is likely to have been cold set to a wider spacing at some stage. My frame doesn’t have any curve in the chain stays, and so mine was originally made with a 120mm spacing.