I got mine installed last night. Due to the great guidance above, and from the other threads, it was a piece of cake. I think it took around an hour, and that was taking my time. I think the most unnerving thing was continuously making the cable hole larger to fit that junction rubber piece.
I did notice that this thing really shakes around alot until you get over 2,000 rpm. More so than on the bar mount, from what I can recall. Seems weird because it doesn't look like the fairing moves around that much? I just hope it doesn't rattle the thing to death! However, it turned out the gap between the HD mount and the dash was far enough I don't need that clear tape to protect the inner. I think it's a good 1/8", plenty of clearance.
Also, instead of paying the big bucks for the Tourtech, I read about adding a teather on the Zumo forums that looks like the hot ticket, at least until I work down some of the other mods on my mile long list:
http://www.zumoforums.com/index.php?topic=11772.0Beyond this, I think it would be nicer if it was angled a little better towards you. Seems a little down and out. I think I will try to add a couple of washers on the back of the Garmin mount to shim it a little. I figure there are plenty of thread left on the mounting screws so if I put 4 washers on the lower left, and 2 washers on the top left, and 2 washers on the bottom right, that should move it a bit more in the right direction. Once I get it right, I can cover the gap with a thin bead of black silicon or something to pretty it up.
Nice mod - thanks for blazing this trail guys!