Tim,
If I understand, you ARE making a temporary repair so you can continue summer cruising....?
why not continue the curve of the rudder to the shaft. In other words: jigsaw the 'square top' into a curve - so that there is NO FLAT OF ANY KIND to hang up the anchor rode on! And if your temporary repairs are fairly smooth and hydro you can get a feel for the missing area. It is MINOR but must be important because the master left it there in both the ear shaped rudder and the constellation style.
So that even if the anchor rode is pulled across the rudder - which is also pulled hard over - the rode will have to slip!!! So that even if the rudder is pulled out at right angles to the boat like a barn door, there is no ledge for the line to hang up on. Only curves. Have to make it so that line will NEVER hang up the way you describe again!