I just completed a couple of additional modifications based on others feedback. First, I switched to braided line. Now that I've tested this fishing, I'll never go back to wire. The difference is that the downrigger line hum is virtually eliminated with the braid. I understand that the blow back is also reduced, but what I really wanted to do was to cut down on the hum. Second, I shortened the boom by 8" from the original length of 16". I could have gone shorter, but was I didn't want to cut too much off... I figure I can always cut more, but I can't make it longer. Finally, I added a line with a "D hook" so I could clip the ball to when not in use. I just looped a line over the drain pipe. My thought was that this method would be snag-less and removable, too.
I haven't tried the shorter boom, but I think I will like it. If nothing else, I'll be able to reach the downrigger line easier.
I have tried the Scotty rod holder next to the drain pipe and this is now my go-to rod holder. It sits the rod out in front nicely, and I can easily see the rod tip without craning my neck. I will keep the rod holder on the Cannon downrigger as I have been using it as a convenient rod storage if I need it (not when I'm using the downrigger, though).
Once again, I can't wait to get back out on the water and do some more fishing with it. Here is how the rig looks now:

