take a look at the photos in the photo section of your year airstream.. but should be tear drops, and bargman round (two singles) in the rear... if you look at vintagetrailersupply.com you'll see some sources. I can't remember if the 50's have the "wedding cake" or the recessed like modern semi trucks have. Either way, get rid of those rectangle things in the rear!
Don't worry if its not totally original, you have some non-stock windows on it already (the round one on the street side). Kinda cool though.