LACSA flys LAX-SJO or at least the planes usually have a LACSA insignia on the side. I would not count too much on the aircraft being a 319 it could be whatever they have the day you are flying. More than likely there will be 12 seats available in business class. I do not like the bulkhead seats because they have less leg room than others. I have made seat reservations several times only to find out they were lost. Best to arrive early to claim seat.