-JdK- A very nice picture of a Model 18 Norton and sidecar; the registration identifies it as a motorcycle that lived in the Dutch province of "Noord-Holland".
The angle at which the photo was taken is spot-on as it provides a good view on a few interesting parts. Note the Horton front hub and what probably is a Norton (as opposed to Webb) front fork; it has the (rather poor) Norton-type of damping, not the Webb-type with wingnuts.
The pics below show what I think could be an identical 1931 front fork girder. Parallel legs, one grease nipple on top, one continuous casting on top but without the lugs to mount a headlight, right-hand brake anchor. c1930 girders are a can of worms however and it could be Webb or Norton; suggestions welcome!