I have a couple of questions for you...
Why a 404?
Have you ever had a Unimog before?
Are you mechanically inclined?
You will probably need to replace the brake lines (they are rubber and collapse internally with age), rebuild the carb, and replace/rebuild the master cylinder. These are parts that when a 404 sits for awhile typically need to be replaced/ rebuilt. Do you have any friends that have a Unimog? If so I'd ask them to go check it out with you.
How much is this person asking? Don't worry I live in VA and have no intention of adding a 3rd 404 to my collection.
Do they have a title for the 404?
If you want to PM me the 40411..... VIN number I would be happy to look it up for you and make sure that it's truly a '58. When I bought my 2 404's I was told one was a '67 and the other was a '69. Comes to find out one was a '63 and the other was a '65.
Also you will probably want to become a member of
Unimog - Benzworld.org - Mercedes-Benz Discussion Forum in addition to your membership here. It is a Unimog specific website with lots of very valuable information.