Here is a full level hack which also incorporates most of the graphics being replaced. Some of the enemies have been redesigned to have different behavior for an additional challenge.
Super Mario Bros. (World).nes - NOINTRO
CRC32: 3337EC46
MD5: 811B027EAF99C2DEF7B933C5208636DE
SHA-1: EA343F4E445A9050D4B4FBAC2C77D0693B1D0922
SHA-256: F61548FDF1670CFFEFCC4F0B7BDCDD9EABA0C226E3B74F8666071496988248DE