I made the dog bones out of 1-1/4 x 8 x 8 sheet of Delrin. I measure the distance I wanted the pole away from the trolling motor shaft. The lower is different because the step down size in the trolling motor shaft. After that I measured the shafts so I could get a hole size, I then cut the Delrin in half, and proceeded to cut the holes in each end with a hole saw in a drill press. After that I used a band saw and remove some of the side material to give it the "bone" look, the drilled and counter sunk 3 holes for 1/4x20 SS screws and lock nuts. Then I sanded around the sharp edges to round it all off. Final was cutting lengthwise down the center with a band saw so to have 2 sides. My holes didn't come out as perfect as I would have liked so I had to sand the inner part of one of the bones to get a tighter fit. All in all it took a few adjustments, but it works. I guess I should have taken some construction pics, but the product actually shows it all. Hope this helps
If you have a CNC shop local they can fab you some out of aluminum. If you get to it before I patent mine