Go to the search tab on this forum, and type that question in. You will be amazed at what you will find.
F9 but man thats some big time rust!!
Primer and paint.
First determine how the rust got there, if the problem is not fix then the rust will just come back. Second determine if its even worth it to try to remove it, sometimes its better to sand and paint.
Use what ever removed the L
On a much smaller scale I have had great results using Rust Remover Plus.
Call Craig at http://www.front9restoration.com/products/. He will be able to tell you how to handle that.