The existing transom knees were oak. I wasn't happy with the irregular shape, or the grain running in the wrong direction (fore-aft). Knees should have the grain at a 45-degree angle across the joint.
I decided to make new knees from plywood. While hardwood is preferable, 1-1/4" thick Baltic Birch should suffice in this application. Here is one of the new knees next to the old ones:
The simplest way to shape the knees was using my MechMate CNC router. I designed the shape and cut it out of 1/2" plywood.
An oversize piece of 3/4" ply was glued to each knee. After the glue dried, the excess was cut away with a mitre saw (straight cuts) and a flush-cut router bit (rounded edge).
To match the bevel at the transom, I clamped a piece of wood next to the knee, and measured the angle. These cuts were made on the mitre saw, with the workpiece very securely clamped.
Test fitting the knees, and deciding on a location for the stern cleats:
The mounting screws were installed from outside, including on the transom. With the transom painted, there was no need to avoid recessed hardware on the transom face.
The knees, glued in place. The two small holes are for the mizzen sheet bridle. The patterns of four holes are for the stern cleats. The one large hole is for the stern navigation light.