[Phlogiston]

I would strip the chassis as much as possible and try some navel jelly on the rusty areas. A lot of that is just stain, Some will be pitted.

The problem with blasting it is that once the plating is removed it will rust again and this time all over. So unless you paint the chassis the rust will return - worse. If I had a chassis that was not originally painted and determined that painting was the only option, I would look for another chassis.

Sometimes I apply a little silver paint with my finger on the rust (after cleaned) just like stain. Wipe off the excess.