Hi Alex-
Avidyne does not put their installation manuals on line, at least for the general public. If you contact their support folks by email or phone and identify yourself as a homebuilder, they will send you one for free via email PDF. The manuals are very thorough, with wiring diagrams for a wide cross section of installations. As stated above, it is designed to be a slide in replacement for the G 430 so any 430 tray will work.
As to the decision to go Garmin or Avidyne, consider the 175 is only certified for planes up to 6,000 lbs. The Avidyne can be installed in far more planes; I don't know the why of it. 90% + of the 175's functions are touch screen only, while 95% of the 410's functions have multiple ways to be accessed via touch screen, knob, and/or button - pilot's choice. If you have ever had to reprogram a full ATC reroute in turbulence, you'll appreciate the difference. Also, check out Avidyne's *FREE* IFD 100 iPad app. Garmin has nothing like it.
Ken