I am with Xrunner.
Well, personally I would not go for the plane, but that is not very important, you are not building it for me. I think to make the plane look nice up there you should go with the photoshop that Xrunner did; it seems the best for me. I think dipping down the front of the "nose" would also help, like in the Photo. You could still install a window, it would just be smaller. Of course this would mean more work, to fab up that change in the front.
I think if you are going to go with it, it will make a great space for a bed without being in the main body of the ambulance, which I really like. I presume this would also require you to cut into the box that is between the ambulance and the cab, to keep the bed space, yes? Not sure if you are willing to have that space taken away from you or not.
Will the door in the plane remain functional? That would seem to be pretty cool, plus make for great ventilation when the time is right.
If you decide not to get the airplane up there, you could always do a fold out bed off of the rear of the vehicle, or one of the sides etc. They always seem to be nice in my opinion. Of course the heat goes right out of them in the winter, still a nice idea if added space is desired.
"Do you know what a soldier is, young man? He's the chap who makes it possible for civilized folk to despise war." -Allan Massie