The first ChromeOS devices shipped with Intel Atom processors with Pineview cores.
These models do not include general purpose bootloaders in their factory firmware, custom firmware is not generally available for them. Consequently, GalliumOS cannot be installed on these models, but you might be able to install an older version of Ubuntu (14.04) using the older ChrUbuntu script.
One possible exception is MARIO. See below.
Google Cr-48 (MARIO)
There is a third party firmware floating around for MARIO. Reports indicate that it works with GalliumOS.
See https://cr-48.wikispaces.com/ for details, and let us know how things go!