Here is a ROM hack for Wild Gunman which changes the outlaws into undead characters and also the backgrounds.
Wild Gunman (World) (Rev A).nes - NOINTRO
CRC32: 330F53EE
MD5: 5B265168D8AFEE1F43535FEA4059AA10
SHA-1: 2A5C4F43A56A4C7A4CA73C4F3EE204AE0FBD8157
SHA-256: 5C993B37F2065812F88244D02EBCC0C4D03472B3116C5C8A132B98229360F8A9