Missing decals is hardly mint condition. Those old decals held up pretty well, so if they're gone the motor must have seen some reasonable use.
American Outboard & Salvage carries water slide decals, which are the closest to the real originals. However, they are expensive and not for a beginnner to apply. Vinyl decals (stickers) work better and only a real aficianado can tell the difference. They all need topcoating.
Try oldoutboarddecals@gmail.com I bought an awesome set of vintage Johnson decals from them earlier this year.