the A12 gear will work on the head ... valves you can stil buy new from nissan or aftermarket as well.
the A12 valve springs could also be used but you'd be better off buying a set of double valve springs new, especially if you're planning on running the bike carbs you'll be wanting to get a fair few revs out of it

good question about the "was it all working before" on the electrics front ?? what were you doing when it stopped working ??