I have just fitted this rack, cost me arm and a leg from the states.
Have also fiitted a back rest(sissy bar,- dirt cheap of ebay), similar mounting idea to yours.
Just to add have also fitted goldie style silencer,@10 deg.,crash bars, small fly screen, headlamp peak, mud flaps, and small saddle bags back and front. Cost me plenty (good old credit card), but bike looks 10 mph faster.
Cant wait for warmer weather.