You might be thinking of Resorcerer (apparently still available for purchase), which was like a beefed up version of ResEdit and included CODE disassembly functionality.
Macintosh Garden has some screenshots of the older version.
Apple also had a CODE editor for ResEdit which was sometimes distributed as "Super ResEdit"
The MPW toolchain for Classic Mac OS which was available for free at ftp.apple.com comes with the DeRez tool that can decompile resource forks: http://mirror.informatimago.com/next/developer.apple.com/tools/mpw-tools/commandref/derez.html
The internet archive has a backup of the ftp site for historical purposes, but I can't confirm the url as archive.org is ...