I used a 44gl oil drum many years ago when I was restoring a 26 Dodge 4, most parts went OK. I left them in usually about 7 or 8 days, washed them off with warm water, then hit them with under coat for protection. Some of the more rusted parts were pitted slightly so they needed a little bit of extra rubbing to smooth out, but all the rust was eaten out.
Just as well those older cars panels were thick, at least twice as thick as todays cars.