Jason, do as you thought and manually scrape what can be scraped; then, go to Princess Auto and buy one their braided wire cup and flat type brushes for a 4" angle grinder. They sell the grinders on sale for about $20. Use goggles and GOOD leather gloves and HOLD ON to the grinder when using it. Between the 2 types of brush, you should be able to clean up 80-90% of it. I've used them to remove all sorts of the factory schmutz and they work. It's tiresome and dirty, but it'll do the job. I'd use brake cleaner to wash off the small ****e remaining before any painting. Good luck! Ian