When I bought the new number decals from Decal City, I also bought their citrus based decal remover. With a hair dryer [it was only 55* outside] I pulled off the old numbers and used their decal remover to remove the leftover adhesive. They also sold me some quick-tack that prepared the surface for the new number decals.
The new Allison Gold decals look great against my royal blue boat. The new metallic gold number decals are a great match for the new Allison decals.