I've found out that a lot of people say that ships are SFC3 compatible that don't have all of the SFC3-specific files. You can take any SFC2 ship and add it to SFC3, it just won't have good vessel library or tactical displays, damage textures, or a ship description. Also, the hardpoints on the model might cause the weapons to fire from odd points, but that really has more to do with how you enter the ships information in the DefaultCore file.