The rust itself should come off a treat, only thing I'd be worried about with the poles being flush is catching the Pup body too and scuffing it. If you can find a way of masking the rest of the area it'd be ok. Not knowing much about the construction of Pups themselves, I don't know how easy it would be to take the top of the casing off. If that's possible it'd be easy to rub the rust off that way.
By the way if anyone thinks this is very very wrong just tell him not to listen to me, hehe. Me being a job-botcher I usually get by on doing Cowboy jobs on DIY at home and on Guitars, there's probably a right way for doing this, heh.