This is my first draft, made in Tinkercad.
Just print the same bckaet out twice, however, I am working on another bracket that holds the USB Dongle.
I moved the top/side bracket back a bit (when mounting to the wall), so that the keytar won't fall out easilly, but how you install it is up to you.
The angle on the Keytar is is @ 15/16 degress if that helps.