Interesting. I noticed the two empty bolt hole on the top fin. Did they originally have a plate there? My kaama drives have the plate. I have heard it will run faster without the plate. I haven't tried it yet.

The upper cavatation plate is not needed.
It will not make a difference in speed.
That portion of the drive is not in the water.
The late model Arneson ASD8's dont even have
the upper skeg;)