Assuming that the auto is a 904 the lenght will be correct but you will need a new slip yoke for the front of the drive shaft. The A833 tranny has the same size output shaft as the 727 which is larger than the 904.
According to my Mopar Chassis Manual the 904 and the 833 in the a-body have the same length from engine block face to end of tail housing (well almost there is .080 difference in length) not enough to worry about.