1964 12 bolt posi interchange?

[Captainfab]

Any posi unit from a truck 12 bolt will interchange into the housing. The difference in your '64 will be the 17 spline axle shafts, unless someone has changed them. Starting in '65 the axleshafts had 30 splines. To my knowledge the Dana posi units were available in 17 splines only. At least the ones I have are all 17 splines. Starting in '65 the Eaton posi units were available. When looking at a Eaton posi unit, be sure to get one of the correct series for the gears you plan to run. The 3 series are for the 3.42 and lower numerically, and the 4 series are for the 3.73 and higher numerically.