Texas Jan, I used Evaporust on a rusted faceplate and needle plate of an old 66's and it really did a nice job. I am not sure if you want to use it on the entire SM or not as it probably will take off the existing finish.
If you are interested, here is a video on you tube:
http://www.youtube.com/watch?v=PWQZCJDBe14
Hope this helps.
Judy