727 -> 904

Well not only will the driveshaft need to be retubed you'll be buying new u joints and a slip yoke as well. The dipstick tube is not the same either. The linkage and arms maybe OK but the flex plate is probably different as well. It's not as simple as it sounds. Rebuilding your 727 and buying a converter for it are better options. The pan is just icing on the cake, makes it sweeter but is not needed.