As others have said, Delta cannot force inventory on partner flights. The 7:05 AM flight from SAN-JFK connects with an early DL operated JFK-FCO flight so your layover will be just under 4 hours. If you are flying in the Main Cabin, there appears to be the ability to get 4 seats together especially if rep will allow you to be rebooked into the "preferred" seats without extra charge (23D, 24DEF on first flight, 21CDE, 22E on second)