There's too many variables to expect a valid answer based on other people's experience. Drop the pan and visually look at the bottom of the dipstick. The full mark (at operating temp in neutral) should be about an inch above the the rail that the pan bolts to. Add whatever it takes and make sure the trans is HOT before you top it off. Temp makes a significant difference on the dipstick. There is no exact level for trans fluid in a 727. You want it above the filter at all times but not overfilled. That can cause aeration or blow fluid out the vent.