If memory serves, primary difference between classes is thickness of pressure hull, not readily visible on models.
No. The difference in pressure hull thickness and steel formulation took place between the Gato and Balao classes. The Tench class had the same pressure hull thickness and increased diving depth as the Balao class. The difference between Balao and Tench is below the waterline. The Tench class lower bow does not gradually curve upwards, as on the Gato and Balao classes, rather it stays horizontal and then makes a sharper knuckle turn upwards toward the bow. This gave additional forward torpedo storage space.
Thank you, Lars,