I now have it working. I had to completely rewrite the paths in the plugin to work with the mac.
I still don't have the path to calibredb which is currently /usr/bin/calibredb
to get the app to work I had to wrewrite usr/bin/web2lrf to /Applications/calibre.app/Contents/Resources/loaders/web2lrf
and similarly rewrite the path to Calibre and the output directory.
If anybody does have any idea where that calibredb file is, it would be good for me to link to it i guess (although all is working fine at the moment).
Thanks ccadi for the link to this.