@T.Albers I will get the measurements from one of my dome cars although I cannot guarantee that they will be scale accurate for your purposes because the cars are nearly full-1/48 scale at 21” length. The domes appear to be separate plastic moldings (see photo below) but unlike the first run of 21” ABS dome cars, which were non-prototypical, they are not just snap-fitted into the rest of the body shell (and on my project I avoided trying to take them out). I think that they may be slightly smaller in proportion compared to your line drawing above but certainly the best effort made to date in 3rail O scale - not even GGD has done anything similar.
