Hopefully you know that the 727 will take, eat, a little more power than the 904 will, correct? You will probably need a 1972 or 1973 only 727 340 small block externally balanced torque converter also due to being those motors were externally balanced in 1972 and 1973 only
The driveshafts are shorter on the stock 727 cars also so you will need to get the correct length and one with matching U joints ends for your rear end pinion yoke and to work on the 727 tranny output shaft also