I think you want Delrin-
https://www.mcmaster.com/#delrin-(made-with-acetal-resin)/=1cobqnn
I just did this with two hole saws and it worked perfectly. I put one shim between the rudder stuffing box and quadrant. This reduced the gap between hull and rudder, but moved the quadrant up even more (the stuffing box had been moved up higher when it had been re-glassed in place by a PO).
You might want to check to see how this wire angle would change with additional shims. In my case the shim has increased the misalignment between the quadrant and the steering sheaves, leading to the wire rubbing on the quadrant when the wheel is turned. I am going to live with this for now and grease the heck out of it. Eventually I may need to go with smaller sheaves, but that would probably require re-terminating the steering cables. I'll check for wear frequently.
I also understand that the factory originally put a shim between the rudder and hull. I tried this but it bound up and prevented the rudder from turning more than 45 degrees, so I removed it. I think the top of the rudder post hits the upper bearing cap so it should not ride up and contact the hull. Hopefully this will not cause too much binding when the boat is splashed and the rudder floats up. We'll see.
Good luck with the project.