If Duncan told you to run higher octane, you had better heed their advice. They know their stuff and they know what their motor will need. If you short change that motor on octane, you’ll be rebuilding it in no time.
Works is back up and running, so you should be able to call them for parts or to have them serviced. There are even a few other guys that service the works stuff and have been making their own parts for them.
As far as that throttle cable, you’ll Definitely need a cable for those carbs, and possibly even a set of the taller adjusters that go in to the tops of the carbs. Those can be found at F.A.S.T.