The iwork 12 will only have the same screen, battery, wifi and external build, the most relevant hardware(SoC, SSD, …) will be different even if on the outside they look the same.
And you should be able to backup the original OS as long as you can boot from a usb drive. Just create a bootable linux usb with enough space and use dd with the output set to a file in the usb itself. There are plenty of guides and forum posts about how to do just that, for example https://wiki.archlinux.org/index.php/disk_cloning#Create_disk_image .