I don't do Airstream renovations. I love to watch from a safe distance on the forums. I'd look at the vintage site to see all the layouts that were used in your year and length, pick the rear bedroom you prefer, then ask yourself ONE question.
Would I be better off selling this one, and looking for another one with a rear bedroom, or would I be better off renovating this one?
Do what your head and heart tells you is best, but if you DO find the factory layout for the rear bed model, you'll have a pretty good guide for doing the changes if you decide that route is better than a sell/buy strategy.
Paula