I soaked a set in POR 15's rust remover. Worked well on the rust and did not damage any existing paint.
Still haven't decided how to seal them and keep them from rusting more but was happy with the results.
If you go with a similar (chemical) treatment, just gently scrub the scaled rust away in between applications and keeping soaking until you are happy.
http://67-72chevytrucks.com/vboard/s...d.php?t=823571