Nice job jimi!
My first fin job was putting a steel strut on the original bi-fin, I included it in the first photos of my fin design I put up a while back but the pictures came out massive and too hard to view.
I tried it out and then tried my fin out and preferred mine so never put it back on.
When you put the strut through the top of the rudder, did you file it so it had two flat edges (like a flat head screw driver) then slide it into a slot into the top of the rudder to make sure it can't twist?
I did that then screwed on a SS nut on the bottom, using super strength epoxy on all of it then coating it in fiberglass. Strong as *beep* (I'm self censoring now). However, try it out and keep building your own designs, it's fun