The quickest way to get the rust and paint off of the area is media blasting. Not an option for most folks, I know. So you'll probably want to start with 600-grit sandpaper and clean it up as much as possible.

If there is a crack, the frame's going to have to be repaired professionally, since it's made from the Reynolds 853 heat-treated steel. Not every backyard mechanic with a TIG welder will know how to handle it - and rumor has it 853 is a ***** to work with.