3M makes a decal and bumper sticker remover in a spray can available at auto parts stores that works very well. I don't recall the name of it, but the guys at the store will know, especially if they supply body shops. It is intended to remove all sorts of stick-on stuff including the fake wood grain stuff they used to put on station wagons.
Automotive paint suppliers sell a round rubber(?) compound disc that can be chucked into a drill. It does an efficient job and leaves the finish unscathed. A little rubbing compound will bend the area, if needed.
Then there is always the heat gun approach. Use a heat gun to soften the decals and glue then remove. Chase after the left-over glue with 3M Adhiesive remover and cleaner.
Decals that old are usually baked on by years of sun and engine heat.The electric sander is the only way to go.
I tried the heat gun and decal remover on mine without much luck.The sander cut them off in just a few minutes.
1981 ChrisCraft 210 Scorpion K,175 Johnson SeaHorse
Peel off what you can and soak it down with goof off..then user a plastic scraper to remove. when they are all off use more goof off to get rid of the adhesive. I did this with a 15h merc and it came out perfect