I'll start off, although others surely know more than I.
From your photo:
I = International trim level
27 = 27' long ball to bumper which is the Overlander
9 = Would signify a 1979 model year
J = Built in Jackson Center, Ohio
Here is a link to the Airstream Inc webpage that decodes serial numbers. I can't make out your photo entirely, there seems to be missing digits in your serial number tag.
Hope this helps. Front, back, sides photos would be helpful.