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.

• The base plate is made from a flat profile 20 mm, 4 mm thickness, 74 mm lenght.
• The support arm is made from an L-shaped profile, 20 x 20 mm, 3 mm thickness, 130 mm lenght.
• Two cylindrical spacers are placed under the base, the outer diameter is 16 mm, the inner hole is for an M8 bolt, i.e. an 8.2 mm hole. The front spacer is 20 mm height, the rear one is 14 mm.
• The RAM-Mount compatible ball is fixed with an M8 bolt and a selt-locking nut.
• Two M8 bolts are required to fix the holder to the top bridge. They are 60 mm length, with the threaded part at least 22 mm.

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:

• An OpenSCAD model. It contains both a 3D view of the complete object and a 2D outline from which you can print a measures reference sheet.
• A PDF file with the measures. It can be used as a reference to cut the iron profiles and to drill the holes.

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: