I used "Oops" to get the adhesive off, worked quite well.
There were spots where there was some rust coming up through the paint.
I used 600 grit wet/dry to clean up the rust, followed by a complete wipe down with "Oops". And not knowing if it leaves a residue, a wipe down with mineral spirits. I didn't pay much attention to the back, I was more concerned with where the sandpaper goes.
Anyway, now, it is entirely smooth, at least as far as my fingertips can tell.
Before I put the velcro conversion disc on it, do I need to do anything about the few little spots where the paint's no longer intact? Will the adhesive from the conversion disc cover it and protect it from corroding again? Should I paint it first? I can't wax it, the adhesive won't hold. Or will it take twenty years to corrode again and who cares
If I paint it, I'm concerned about getting it smooth again. I might have to do a few cycles of paint, sand, paint, sand