I've found several for sale with 4 place intercoms which tend to indicate 4 seats.
Found this ad http://www.airliners.net/open.file/0048724/L/
Interesting note I found in another story is that same owner died this year when he flew this plane into a major thunderstorm. Plane disintegrated about him in flight. Debris spread across 3 fields. Former X-15 test pilot. Should have known better. []