Jeepers, sorry I never noticed your post! Obviously, there is noemail warning of a message here. My apologies!
The newer the AS, the higher the ceiling, it seems to me. They eventually found that the low bulkheads separating the lounge area from the sleeping area and bathroom is NOT fun to run into.
Also, the ceiling lights and air-conditioning units got slimmer on the interior too. For your own health, I recommend an '80s or even better, a '90s model. Your head will thank you. They really don't cost that much more either, I have found. And it is more certain that a '70s model will need more work than a newer one.
ps: I always wear a hat for the first few days we camp in it. It has saved me a good deal of skin!