There cramfs tools for Mac OS X (PowerPC version NOT INTEL - there is word endian difference).
Xcode project - compile and get utility to run in terminal in root user.

some my modification - cramfsck - when unpack cramfs volume - store all file attributes,user,group to special file called 'rights'
mkcramfs - build new cramfs volume and set file attributes depends on 'rights' file created by cramfsck.

So, in rebuilded cramfs - we got original file attributes,user ang group owners.

download from here - http://www.filefactory.com/file/955d27/