I am wondering if, like Lepke posited, the metal bracket is/was intended for a more robust bearing system. Interesting/odd that multiple members here have the same boat with the same, apparently unused bracket.
Is it possible the metal bracket is intended to have the shaft collar located on top of it, thereby helping spread the load onto the wood shelf? Perhaps a PO changed it for some unknown reason (I know, on multiple boats the same thing happened?)
Our boat is NOT an IG, but does have a very similar constructed boxed plate that is the mount for an upper rudder bearing. We have a shaft collar too, which is above the bearing.
In looking at some online drawings of rudder stock design, there is a piece that tends to be in that area of the rudder stock, and its called the carrier but has a bearing in it in each case.
In the OP's photo, you appear to have a shaft collar under the metal bracket, and is that a large flat washer under the shaft collar? Is there a bearing in the wood shelf?
Excuse the leaked and not cleaned up grease, but here is a photo of our rudder stock / carrier assembly for reference...
At the very top of the pic (you can only see a portion of it) is the portion of the quadrant that is mounted onto the shaft. Below that is a shaft "collar" that consists of two halves that bolt onto the shaft. There is a bearing mounted into the SS plate (you can see a couple mounting screw heads.) Finally below the plate is the packing which is mounted on a reinforced fiberglass mounting area glassed onto the hull. This is a boat with hydraulic steering, BTW.