2020-04-19: Time to cut the rudder.
Although I had measured the dimensions long time ago I rechecked them to be absolutely sure that they are correct (measure twice – cut once!). I adjusted the cut line at the bottom of the rudder according to the instructions for perpendicular hidden bellhorns.
First cut on the outside:
Next cut on the inside.
Used the multitool to cut the skin, then a hacksaw to do the final cut through the foam.
Then I removed the plug. It was a tricky process to get it out, but the end result was good:
Finally I inserted the rudder cable and mounted the AN111 Cable Bushing as several other builders have used – this is a much neater install.