My boat also has the drain hole in the sole forward of the mast apparently similar to yours. It seems to me that getting the water out of the mast and as directly as possible to the bilge would be an advantage. So drilling though the casting might be the best. The damage to the sole in this forward area of the sole happens on both sides of that drain hole. I know there are multiple other sources of water here besides the mast, but that is likely a very big contributor. Once I repair the Holly I think I will use some CPES on this area in an effort to slow down the decay.
As to the turnbuckle I will defer to anyone else that may have an idea about that. I can only say it was there when I bought the boat.
