For my own information as well as yours ...
I took some fotos of the steering on a trike made by S&B Recumbents. This steering has also been modified for the use of a tiller-stick over-seat steering.
This is an overhead view of the steering mechanism.
It uses a round tube at 90 degrees to the main tube.
I believe it has 15mm axle Phil Wood hubs. It is definitely NOT very massive ... quite petite almost, but designed to carry a 250 lb. person.
Here's a view of a hub with the arm and both linkage rods.
This shows the connection between the steering and the linkage arms. There are additional tubes that are actually frame support members and not related to the steering. Pay attention to how the 90 degree arm is connected with the steering headset.
Note the chain routing ...
As wells as the linkage.
Here's a close-up view of the axle connecting with the headset. Notice the grease fitting.
With everything straightened up ...
This is a view of the bottom of the linkage.