It just occured to me that maybe meow_mx ment PEF Viewer and not PEF Explorer?
If so, there are two versions - one for OS9 and another one for OSX.
The OS9 version I don't remember where I got it from, the OSX version is part of early XCode tools.
The OS9 version works standalone as is. The OSX version installs additional Powerplant framework into System -> Private frameworks.
I hate when something from the old system is installed into newer system, so I made my own standalone version of it by moving the Powerplant framework inside the PEF Viewer app and patching both executables with install_name_tool. Tested and working on Intel with Rosetta and on PPC Leopard.
If someone needs these, I can put them up.