The latest version of Android was recently added to AOSP and almost instantly was made into a flashable Rom for the Galaxy Nexus and Nexus 7 devices. There was no Change log made available so I’m not sure what is different here other than various fixes. JRO03L is still 4.1.1 so Im guessing not much at all has been changed. Simply download and flash via custom recovery of choice. Be sure to wipe!