A '78 is just old enough to be considerd vintage this year. It's still a current enough model that you can often find sales brochures on ebay that would talk about the differences or maybe find someone here that has one and could share information.
The Vintage Airstream Archive
site may be helpful. It gives a visual comparision of models 25 years & older, '78 is included, although there aren't any pictures posted yet. You may want to check some of the earlier years to compare. Not all the options are spelled out but if you spend some time there, you'll get an idea of how different units were outfitted.
Also the Model Heirarchy
thread went into some folks understanding of what was included in the International package.