...There is a gap between the outside diameter of the mast, which of course is round and the inside diameter of the step, which is square. I have read that you can add wedges fore or aft of the mast at the step to add or remove mast rake.
From the above statement I'm wondering if you're confusing the term "step" (which is the base that the bottom of the mast sits on) with "partners" which is where the mast passes through the deck. Your side mounted brackets will be to support the deck as mentioned above. Wedges are often added around the mast to lock the position of the mast in the partners. Depending on the design and intent of these brackets, wedges may be reduntant.