I'm not sure how far Gastons is below the dam, but from the dam down to the state park is closed fising this time of year and the state park area is catch and release.
There are several places to launch a boat or wade on the White. Two very good books for locating fishable water and access are 1)Home Waters and 2)Flyfishers Guide to Missouri and Arkansas. I know Home Waters is available at Blue Ribbon Flies, and I think I bought my copy of Flyfishers Guide there too.
As for fishing Norfork, there are just two accesses on the river. The boat launch below the dam and the Ackerman Access. Only the dam access has a boat launch. There is an access on the White just below the junction of the White and Norfork. Not sure if there is a boat launch there, but you can take out there if you float with a kayak, canoe etc.