Pivot hinge with fine adjustment for vertical on the pin.

[Toolmaker51]

That ocean does funny things with vocabularies. Plummer blocks there, pillow blocks here, neither being something I'd wish to lay my head on.
I didn't visualize the remainder very well; tensioning the spline while inserting the normal way is a time consuming exercise. Building an assembly machine beats waiting on evolution supplying us with a third arm.

The three screw arrangement might benefit, if set to bear on a bushing supporting shaft in question, though a four screw mechanism is probably easier to manipulate.