Use generous amount of xylol and a cotton towel, xylol will melt the adhesive, if the adhesive is thick it will come off in layers, do like a 12x12 section at a time. Once the towel gets saturated with the adhesive use a new towel or keep going to a new section of the towel. It will take that metal down to like new, it will completely remove all of the adhesive. Wear gloves and a mask, I use nitrile gloves but I used to do without both when I was younger. There is nothing anyone will suggest that will work better than xylol, and out of all the solvents xylol is the only one that will work. I have been taking off decals and adhesive for 35 years, have tried everything, and that is the one that works, and very easily.