We replaced the 1974 Bowen 10 gallon in our Sovereign
last fall, and the main difference was that the gas connected from a different spot. We bought ours on sale at Camping World ($399) and had Airstream Service in JC put it in while we were having some other stuff done.
Anyway, the existing gas feed wouldn't work, and I -think- they had to re-route it to come in from below, and the original inlet came from the side, IIRC. I see it when I light it every time we go to the camp where it lives (which was last Thursday (getting home yesterday) but who thinks about where the gas comes in? Like I say, the important thing was that it required more time, due to being moved.
Also, where the old tank was visible (and galvanized I want to say, NOT SS), the new one is covered in foam. This saves heat, I would imagine.
Oh, and it also required cutting out a strip on the bottom side of the opening, since the new frame was taller. The cutting also meant that (for now) I have the cheap-looking beige door that came with it, and not the nice SS one that was installed originally. I kept the old door, meaning to some day put it back on, but when I came across it in the shed on the weekend, I also noticed that the rectangular grill that allows the exhaust to escape was part of the old heater, and not part of the old door, as is the case with the new one.
So, yes, the best fit it the new Atwood (they bought Bowen years ago), but that's not to say it just slides in and bolts up.