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I was looking for a way to de-rust the brake discs, also the internal cooling. Today I was watching "Cafe racer" on Discovery channel where they showed how the petrol tank of a Norton bike was being derusted using an electrolyte nd a battery charger. This looks like a real easy and cheap way of de-rusting that can be used for the brake discs too. See als the following article:
http://www.htpaa.org.au/article-electro.php

Speedtoys

So...theyre gonna rust again.

Mrmerlin

buy new brake discs,
remove the cosmoline with brake cleaner,
then paint them with hi temp engine paint,
OR buy coated brake discs ,
Zimmerman makes these,
they are coated with a silver finish,
and the brake pads will wear off the finish where they contact the rotor,
the rest of the part will stay clear of rust

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All true, but the message reaaly is that this may be an easy way to de-rust metal parts. Her in the Netherlands we have a lot of rain so old cars have a lot of rusty things. Metal brushing doesn't remove it effectively. Bead blasting does but it may be easier to DIY some parts at home.