Definitely the 91% isopropyl & magic erasers for a start. Get a couple of rolls of shop towels and some Simple Green. Make a diluted spray bottle of the SG, but keep the full strength on hand too.
Soak the eraser, start in a spot that may not be so visible, e.g., bottom of side, toward rear corner, and work slowly in small circles and see if the paint starts coming off. Be careful not to go too hard or spread the solution over too large an area in case it burns through the ink on the original art. Wipe away some of the paint with a towel and see if you get a sense of the stability of the OG art with this process. You might want to spray a little of the diluted SG on that area and do another wipe, then gauge the results. Play around to find out what works best, go slow and be patient.
One thing that I found helpful was, while wearing a latex glove, pour some isopropyl on the area to be "erased" and rub it around to spread it out a bit to let it start to loosen the paint bond. Then start in the with eraser. Sometimes I found the initial paint bond would be loosened enough to wipe a good amount of it up, making for a much easier time with the erasers & iso.
Experiment and see what works best but if it looks like the underlying ink is getting affected, back off (obviously!).
I did this with my Defender and it went great, but Williams did a great job with their stencils and that paint is freaking durable! I got lucky with whatever paint was used on it too because it was a light coat and came up easily. I also tried this method on a Deco cab and sadly, the underlying ink was so easily compromised there was no way to save it, though the paint was much, much thicker than on the Defender and it took a shitload of elbow grease to even get to the color.
Good luck...
Also, do some searches for isopropyl, magic erasers, and paint and you should find plenty of info. Hit youtube as well of course.