After much trials and references to the below webpages:
I finally found out sadly that [l suspected this initially since the zip file was for Nexus 6P], that l cant run/push Android 8 aka android oreo to an unlocked old Nexus 6.
I need a Nexus 6P or higher. The creative hacking was fun though… 🙂
See below in case you come across similar issues. Linuxmint 17 terminal console output.