It's critical that you get yourself a Norton Manual............real soon . Make sure it 's for 1975 850cc Mk3 and onwards.
This is a purchace that you should RUSH.
Everything else , DONT RUSH .
Darned good project bike that from what Ive seen so far , there doesnt appear to be much out of place .
Get some plugs into those plug holes, or screw a piece of clean cloth into them , at least by a couple of threads , to prevent anything going down the hole into "nomans land" !
Youve come to the best forum for gathering info and making contacts , good luck with it all.
Supaflee