This is a design for the Shen Drones Terraplane.
Guide for 3D printing the gimbal design here.
Files on Thingiverse: https://www.thingiverse.com/thing:4964713
UPDATE: This design is compatible with the 20mm Universal Mount.
If the Universal Mount doesn’t work with this base or for your application this design is compatible with the 20mm GoPro/FPV Camera Mount Options: