Yes the N7YC is what I have always used and yes gapped at .018 as Joe Hunt recommends but I am running the newer 4 rare earth JH, also you will get very long life out of the plugs, so far I have over 25k miles on my plugs and they look as good as the day I put them in when I first installed the JH, I am putting my old Amal's back on as been running PWK carbs since I been running the JH so all new plugs will be installed although the bike hasn't lost a beat since the JH has been on.
I ran a old Joe Hunt maggie of my 81 Triumph Thunderbird for over 9 years and well over 240k km with out any problems at all and one of the reasons I went with a new JH on the Norton and so far haven't touched it except pulling the front cover off to check on the point's and put a few drops of STP on the felt for the point's cam lube.
Ashley