Greetings, Mklmrck, and welcome to the forums! I'm sure you'll find lots of information here about your Airstream, both general and specific.
Assuming your new cylinders are steel and 30-pound, you'll find that they're shorter than the corresponding aluminum cylinders, but also somewhat "fatter." Oh, and they're a lot heavier, too! If you still have the original aluminum cylinders, they can generally be requalified and placed back in service if they're otherwise in decent shape and have the required OPD valves.
Again, welcome to the forums!