Replacing Front Seal on a 727

68 Dart, 340, 727. The front seal is leaking badly so I'm thinking of replacing it myself. Are there any videos or tutorials on this subject? Would it be better to remove the engine/transmission as an unit and then repair the tranny? Are special tools required? Am I likely to find bad bearings or something that caused the leak in the first place? Sorry for all the questions...............this will be a totally new experience for me.