All of the Super-Turbine 300 2-speeds have the same gearing, 1.76:1 low and 1:1 high. You can use the 326 Tempest tranny if you want. The GTO tranny has one more plate in the clutch pack as well as using a converter with a slightly lower stall speed, that's pretty much the only difference.
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My wife says I never listen to her, at least that's what I think she said.