I've only quickly checked to make sure this would hold the weight of a guitar, please use with caution and make sure to mount solidly to the wall in question.
Designed this wallmount based on my Yamaha guitar, the fit is pretty tight so it might need to be adjusted.
It's designed to be printed upside down so the layer lines are perpendicular to the weight of the guitar.
I've included the FreeCAD file in case adjustment is required.
The author hasn't provided the model origin yet.