I used the dash mount with the 550 on my '09 SG (No dash pad), and loved having it there.....except for a couple issues. 1) I have a KlockWerks shield on my bike....and due to the aggressive flare, I couldn't mount the GPS cradle in the four holes provided on the dash mount. I had to use the lower two holes, and even then, it was hard to get to the release lever on the cradle. 2) Since my GPS was mounted about 1" lower, it obstructed my view of the fuel gauge.....which, as it turns out...wasn't that big a deal since it doesn't read correctly anyway.
Eventually, I ended up getting a HogTunes Tweeter Pod, and moved the 550 over to the HD chrome clutch perch mount (76000191) which I think looks pretty good...much better than the old stamped steel part they used to sell. Here is a picture of the mount I use:

I also upgraded to the 665, using the same mount. But sometimes, I wish I had it back on the fairing just to put it up a bit higher and more toward the center.
When I bought my '12 SESG, I bought the same mount, and use that, but ran across a guy who had a hot citrus inner fairing that was drilled for the dash mount. The dealer scrached the paint while drilling the holes, and replaced it free of charge, so he sold me the scratched fairing dirt cheap. Problem is, I use a KlockWerks shield on this bike too, and I'm afraid it won't work with the GPS mounted in that position. But I'm thinking the SEUC dash pad might move it out just enough to fit.
While searching for the part number of that handlebar mount I have, I ran across a good thread on this forum where Chicago-Spike swapped a new style dash pad with gps model onto his '09 SEUC, and he included part numbers for everything, so here you go:
1106 Screw
1107 Screw
7686 Locknuts (2)
92346-10 Mount (accepts garmin cradle)
92466-10 Retainer (goes inside fairing for support)
57885-10 Pad (dashpad specific to cradle mount, already has holes)j
Here's a picture he posted of the parts (minus screws):

A pic of the final install:

and a link to his original thread:
http://www.cvoharley.com/smf/index.php?topic=50057.0%3BallHe really did a great job documenting the install with pictures.