OK, the package is in the Zone, under the name ECSIcons.lha. I have also included PeterK's library into the installer and the package since it is really amazing. But beware that LoadResident does not work on all systems (it works on my ACA620, but it does not seem to like ACA1232), so install at your own risk, I've just included it for convenience.
Ultimately, the whole installer is an AmigaDOS script so you need a full OS3.1 installation to make it work properly. It's rather clever, only copying the icons you already have and not creating unlinked ones. Also it confirms the major steps.
I also included a whole bunch of whacky backgrounds I created for the colour scheme.
There will be a whole bunch of unused icons in the EXTRAS drawer that won't be copied automatically, so just take a look after the installation has been completed.