That should be a great trip! We outfit a lot of Goodnews floats and invariably hear back about how awesome it is.
For fly line in August on your 8 weight I would recommend a weight forward floating line that can handle large flies. Rio Grand, Airflo Galloup Nymph/Indicator are two that are very good and cast well on a wide range of rods. A sink tip is occasionally helpful for silvers, especially on the lower end of the river, but you can likely get away with a 5 foot Polyleader in Fast Sink.
For the switch rod, depending on whether you are running a head system or one-piece line, a floating line will get a lot of the work done. Particularly for bead fishing. You may use some sink tips if you plan to swing flesh.
One other note, if you have a 9 foot 6 weight, this is an excellent rod for trout on the Goodnews. You may want to keep 3 rods strung up. One for silvers, one for swinging leeches/flesh, and a third with an indicator and bead rig.
For flies, it would be helpful for me to know what week in August you are floating. Let me know and I can make a specific list for your trip dates.
Should be great!