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thanks..!! hope to fond the right gear ratio for my ride

The gear ratio will be the same in all 727's. 2.45 1st, 1.45 2nd and 1 to 1 3rd. As far as which one to get a 71 - 74 would probably be the strongest because of internals and engines in those years had more horsepower. 75-78's would be ok from trucks or HP cars and all from 71-78 have the part throttle valve assembly which will allow wide open throttle downshift to second. Pre 71's did not have that feature.