This version does hold the G1-G3 models the best, but ultimately I came up with this redesign which fits G1 through at least G6 if not all HP mini PCs https://www.printables.com/model/585091-10-inch-rackmount-for-mini-hp-prodesk-elitedesk-g1
The author remixed this model.
This is a remix I designed to mount the unit backward, added holes and elongated the channels.