Just a follow up to my original post. We spent two wonderful weeks in the 500 loop. To get to the Settlement area and boat launch, we just walked the path past the comfort station to the main road and turned right, as suggested above by DavelnTN.
This was our first visit to the campground, and we've been bitten by the Fort WIlderness bug. We literally bought the t-shirts, and we're booked for a return visit in November. Thanks to everyone who offered advice!