Scale and gauge
First of all, it is impossible for a model to be both scales at the same time as these are two distinctly different scales. Although both run on the same 16.5 mm gauge of track, 00 is of 4 mm/foot scale and H0 is of 3.5 mm/foot scale.
Then there comes the question of loading gauge. As we are all aware, British mainline locomotives and rolling stock can be run almost anywhere in the world that uses standard gauge track but the converse is certainly not true. As far as the United States of America and Canada are concerned, their trains do dun on standard gauge track but their loading gauge profile is considerably greater than that in Britain.
The illustration shows two models. One is a British Class 33 locomotive and the other is a North American GP38-2 locomotive. Remember both models are to the same correct H0 scale. As always a picture is worth a thousand words, well one hundred and eighty six words anyway.