Welcome Jack older units are lighter than modern ones. It would be helpful to know the towing capacity of the jeep.
Here is a link to airstream's website which has spec on weights and sizes.
Airstream, Inc :: Travel Trailer Specifications
When looking at older units pay particular attention to the condition of the floor and if possible the frame. Age and leaks may have taken quite a toll on the condition of both.
The frame will be tough to check as the underneath is fully enclosed but look for corrosion around the belly rivets or if it is sagging. That is usually an indication of frame rust.
The floor should be checked all around the perimeter of the shell wher it meets the floor. Pay particular attention to areas below all windows and openings, also the rear area which is prone to leaking. Check integrity of the floor with an ice pick to detect rot.
If you can travel try to get one from a dry climate like CA or AZ. Wet and salt climates are hard on units.
Smaller units will demand more money than larger ones.
Good luck on your search.