Its hard to know whether you will be on an AB6 with the new seats ,there is no way of knowing until you board the a/c. I have only flown BOS-SJU in J and not in Y but the Y PAX had a warm meal last time I flew (April 2005). Service is the same as domestic in J and the only difference is that Y has warm food. If it makes any difference to you, BOS-SJU and I guess JFK-SJU are staffed with International Crews, I think (slugo will know more about this than me).
Matt