From the Mopar Chassis Book (printed in 1990).
All dimensions are from mounting face of bell housing (where it mounts to engine block) to centerline of yoke (center of u-joint cap):
Manual Trans
1. A833 (A & F Bodies) = 34.08"
2. A833 (B & E Bodies) = 38.13"
Auto Trans
1. A727 (for all cars) = 38.13"
2. A904 (for all cars) = 34.12"
With everything else the same (same rear, same yoke size, same car), it means that swapping between a A body 4-speed and a 904 will use same length driveshaft.