I was going to suggest machining the existing 2" bore in the wheel to an SD size taper (2.1875"), IF the hub of the wheel is beefy enough. Then you could pick up an SD bushing with a 1.875" bore to fit your ruddder shaft ($18 from McMaster-Carr
THEN I saw your last post. No way would I recommend doing that with an AL wheel. Also, I think it's not a wise idea to try to cut that wheel into a quadrant. Not wise as in $@&*ing dangerous! If you MUST do this conversion, why not find a good deal on a bronze or even AL quadrant? Around the country, old sailboats are being scrapped virtually every day. Well worth waiting to get the right part, instead of converting from Tiller Steering to Frankensteering!