Welcome to the Forums.
These units were not offered with a rear ladder at the time by Airstream. There was no real need for them as the roof was only rated at 300# max.
A ladder could be added if wanted but probably would require a reinforcing plate on the rear cap where it mounts.
The other consideration was, even though the book said these units were 11'10" high, I believe this and later Freightliner chassis were actually just over 12' if the OEM air suspension is adjusted to factory specs.
This unit that you are looking at has been reviewed on this site previously and is owned by a current forum member.
It is always buyer beware when purchasing anything, and more so when the unit is 18yrs old. Do your homework with consideration of problems you might encounter.
These older units are best left to those people with some resources and abilities to do your own repairs as the shop rates are very expensive.
Now if it passes your detailed inspection, I am sure you will get great enjoyment from camping in an Airstream.
1995 Airstream Land Yacht Diesel Pusher