When I did mine, I got some Scotchbrite pads to do the hand stuff. I also like using the small round pads that look like Scotchbrites but have Velcro on the back and stick to a mating holder and mandrel that will fit in my die grinder or an electric drill. The setup came from my local NAPA store. You can get pads and holders from about 2" up to 4". Replacement pads range from around $2.00 to $4.00 and last reasonably well. I find they do a very good job of getting down to bare metal without a lot of swirl damage and it is pretty flexible for getting into tight corners.
Make sure to wear a mask or keep things dampened down when working in an enclosed cab. That rust dust and old schmutz isn't good in the lungs. Of course, eye protection goes without saying, but I said it anyway.