Welcome to the forums, and to the world of Airstream ownership and restoration!
What you probably have is an Airstream Overlander. That's the model name. Overlanders were quite popular.
The words "International" and "Land Yacht" referred to trim level and equipment upgrades. "International" models had features that non-International versions did not. The highest level was "Land Yacht".
A puzzling fact is that both labels are present on your trailer. Most trailers were labeled "International" or "Land Yacht" but I don't recall seeing too many with both names. But Airstream used all kinds of combinations through the years.
As mentioned earlier, Airstream did not provide owners manuals or service manuals until some time in the 70s.
But there is a ton of information out there on the Internet. A good place to start would be the Vintage Airstream Photo Archives, http://vintageairstream.com/photo-archives/
There is a section specific to Overlanders here on Airforums, http://www.airforums.com/forums/f22/
Finally, I invite you to join the Vintage Airstream Club (VAC) a division of the Wally Byam Caravan Club International (WBCCI). http://vintageairstreamclub.com/
Through WBCCI and VAC you can meet and correspond with hundreds of like-minded individuals, and you can see their trailers and compare notes at rallies.
Best of luck with your trailer!