No*. 900 forks are thinner and longer, with the neck being a bit longer too. Inner fork tube is 45mm (800 is 43mm) and outter tube is 53mm (800 is 55mm). *it could be possible, if you also brought over the triple tree and used the 800's stem. Unsure of inner neck diameter of the 900 at this time. #1.
The Tiger 800 platform has proven to be incredibly robust, and my experience with it absolutely bears that out. My 2011 XC now has over 80,000 miles on it and has needed nothing but the usual consumables. It has been an absolutely stellar motorcycle (and continues to be).
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