I chose a cup shape wire brush mounted into a standard angle grinder. I have heard good reports about the oscillating multi tool with the non serrated flat blade.
Gloves, earmuffs and a full face mask and safety glasses/goggles are preferable. I initially had just safety goggles on and had to pull a piece of wire out of my forehead when I stopped for a break, I did not even feel it go in. After that I put on a shield like a welding mask.
I also tried an air chisel, bad idea, OK on the flat but it made a hole as soon as it got near a moulded section of floor pan.