I would say it's a 1960 - 63 California built 28-foot long Ambassador Land Yacht with twins, most likely an early '63.
Check ths out:
Vintage Airstream Photo Archives
For some reason the '63 Ambassador link isn't working, but the '62s stop with 0315...so 0321 would be a '63. In '64 the number format changed.
Good luck if you decide to get it...you'll find all sorts of help here on AirForums!
Shari
