Here is a patch which converts Gun Smoke's original Mapper from UNROM to MMC3.
Gun.Smoke (USA).nes - NOINTRO
CRC32: 6B8F23E0
MD5: B7323D5CF56F4049E20D44815CA6C45A
SHA-1: 612F2AA339BF1AE54B466F1574752CD753097503
SHA-256: 4AD9629A2BACC158A7F50975869C7DFE533567AE399A5BDC5DF2240286DF259F