According to Alden's "The Fleet Submarine int he US Navy", the GAR was part of the Tambor class.
The Tambor's characteristics included:
307' 3" LOA x 27' 3"
Operating Depth - 250 feet.
The machinery layout is what differentiates them more. The Tambors had a Diesel/Electric system in what Alden terms an E-3 [Engine-Generator Generator-Engine / 2 Motors / Reduction Gear]. Engine-Generator pairs were not coupled.
While the Gato's included:
311' 9" LOA x 27' 3"
Operating Depth 300 ft.
The Gato machinery arrangement was E-4 [Engine-Generator Engine-Generator / 2 Motors / Reduction Gear]
Refer to Alden for more details on the hull framing details between the Tambor other classes.
The Floating Drydock http://floatingdrydock.com/MasterPlan.htm offers numerous plans of various members of the GATO class as well as other earlier boats.