RAM Mounts is famous for its system using the rubber balls as joins, the most effective is the B size, where the ball size is 1 inch diameter.
I built a steel adapter welding together two pieces of standard soft iron profiles. The holder fits the bolts of the steering handle. Here are the measures, a 3D model and the pictures of the final result. The actual phone/GPS holder is a RAM Mounts compatibile one, which integrates its B size ball and the short double socket arm.
This is the final result. The bracket still needs to be painted:
Here you can download some files to help you in making the piece:
To attach the self-made holder to the top bridge of the Revere you need two M8 bolts, 60 mm length, the threaded part must be at least 22 mm in length. I chose the flanged head type.
In these photos you can see the RAM-Mount ball mounted on the bracket and the GPS mount purchased from Aliexpress: