You could try a little heat, like from a hair dryer, to soften up the glue, carefully get a snap-off or X-Acto knife under one corner, slowly peel away sticker using more heat as needed, clean off glue residue with WD-40.
I use a heat gun to remove decals,
keep the heat gun moving and apply just enough heat to warm the decal but not harm the paint.
when the decal gets hot I peel up up a corner and pull gently. you will need to heat and pull several times to get the decal off.
when the decal is removed I use 3m adhesive remover to remove the glue. just follow the instructions on the can
I’m in on all the suggestions, but have found these plastic razor blades a big help. JasonH put me onto them and they are great for anywhere you don’t want to damage a surface. You can get them at any hobby store, Michaels, or off Ebay in large quantities. Give them a try!
That’s a nice motor. Is it an original? It’s hard to find a Chris Craft with the original paint in that good of condition. The idle quality of the Challenger motor is one of the best Iv’e ever heard.