The ad. is referring to the spline count on the axle shafts, not a gear ratio... I believe that ARBs work across all gear ratios, but you should get the part number and check to make sure on ARB's website.
The carrier break is 3.73/3.92 for all D44s, this includes ARBs. But this is not the concern here. Up to '71 the spline count in D44s is 19. After '71 the count is 30. Very early D44s had 10 spline shafts, although I doubt you will find one anywhere. What is the $, I know guys with early D44s?
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