4 speed output shaft

i have a out put shaft from a 3 + od ox and put it on the alumin833 what length do you need? this one is longer than the one for the Dart... i just swapped the tail shafts took the A body shaft off the 4 speed box and put in on the aluminunum 3 + od Box.. so still have the complete longer 4 speed tail shaft complete and together.