Finally (almost a year later) got around to installing the thing! It went very well thanks to the advice on here (thanks!). I put it down on the side around 9 o'clock (audience). It's the perfect spot for how I like my ride. If I had put it in the traditional spot it would have been way too high and angled like crazy. It's still not perfectly vertical with my 22" K on it but it's not too bad.
As for the holder itself, it's a little wobbly but seems to hold fairly well. I haven't given it a full playing situationn test but I'm sure it will be fine. Drill bit size is 8mm or 5/16" FYI.