I don't know about rust, but I've had success with some pretty gnarly cams using the following method.
I put a long M8 cap screw in the end, so that I can hang the cam from the chuck of my drill press. I have a plastic cap that fits nicely in the hole in the drill press table and also fits nicely over the journal at the other end of the cam. I can't recall the exact RPM I use, but it's a medium speed. I start with 600 grit emery, cut into strips slightly wider than the cam lobes, and WD40. That takes the roughest stuff off. Once I'm down to smooth metal I clean off all the WD40 and grit. Then I switch to jeweler's rouge and a soft cloth. For the jeweler's rouge I up the RPM -- but watch the fingers, you don't want that cloth to get tangled while your holding onto it! The jeweler's rouge gives a pretty good finish, which I've used as-is, but you can move on to Brasso or other metal polish if you want a really good job.
Once all that's done, make sure you give it a really good cleaning to get rid of any remaining grit. Varsol does a good job of taking the jeweler's rouge off.
