Finding a coach in the age range that you specify is going to be challenging. During that time a doule-bed was about the largest bed offered. I don't believe that the Overlander was ever offered in a rear bedroom configuration which would have been necessary for a queen size bed. Starting in the mid-1970s, it was possible to find a few Airstream models with rear bedrooms (mostly 28', 29', 30', or 31' models. Even then, most of these were offered as either twin or double. The rear bedroom queen models didn't become popular until the wide-body coaches were introduced, and even then, they tend to be somewhat scarce.
If you are willing to consider Argosy, the 28' and 30' rear bedroom coaches (approximately 1975 through 1979) offered the panoramic rear windows in the rear bedroom coaches, and it wouldn't be extremely difficult to convert one to a queen bed (RV Queen-size) . . . but be prepared for a tight fit. I suspect that if you wish to remain in the pre-1980 model range, you will be looking at modifying a double or twin rear bedroom coach to conform to your queen size bed requirement.
Good luck with your investigation!
P.S.: You can find floorplans and additional information about Airstream trailers of the 1970s at this link