Physically making a CAD model would be easy, yes. The "hard" part I was considering was the need to get spare parts to make the models from, as if the machine i

Physically making a CAD model would be easy, yes. The "hard" part I was considering was the need to get spare parts to make the models from, as if the machine is in use it's a very bad idea to take it apart unnecessarily. And most of the surviving machines are in use. So measuring the old parts would be a bit of a challenge. Also the new, "better" device is a cuirass negative pressure ventillator, but those apparently have the disadvantage of being far less comfortable for long-term use than an iron lung (though much more portable).