Hi Phil, and welcome to the HUBB!
Check out the US State Department website for information, though they tend to be a bit alarmist.
Libya is no go for US Citizens, not for any reasons of danger, but because they're in the same category as Cuba.
http://travel.state.gov/libya.html
"On December 11, 1981, U.S. passports ceased to be valid for travel to, in, or through Libya and may not be used for that purpose without a special validation."
There are no prohibitions by the US Government on Americans travelling to Sudan or Iran. Although we have had reports from travellers of good experiences in both countries, Sudan tends to be difficult to get vehicle permits for.
We know of Brits, French, Germans, Dutch, Australians and Canadians who have travelled through Iran on various visas.
Although rules can change quickly, we generally find that whatever the Embassy in your home country tells you is unlikely to be true. Your success may depend on which country you apply for the visa in, and what border you cross to enter.
For both countries, a search on 'Iran visa' or 'Sudan visa' will bring you a lot of pages.
This thread on Iran visas was current as of last summer:
http://www.horizonsunlimited.com/ubb...ML/000108.html
Good luck with your trip and keep in touch!
------------------
Susan Johnson
"It matters not what goal you
seek
Its secret
here reposes:
You've got to dig from week to week
To get Results or Roses."
Edgar Guest
'One world, two wheels'
www.HorizonsUnlimited.com