Yep, my S2 has an enclosed head (uses a curtain for the door). Keel box on one side, bulkhead behind, and the hull of the boat on the other. Like I said, currently has a port-a-potty, but will likely go to a composting head before too long (likely before we ever use the port-a-potty...). Here's an S2 6.9 (smaller sister ship to the 7.9) that has the same layout. Again, likely comes with a port-a-potty, but the head is enclosed and could easily be converted to composting.
1983 S2 6.9 sailboat for sale in North Carolina