Some missing scenes are there, but not much. Then there is a lot of tech stuff if you are interested - like how they created the hovering helicopter helicopter sound, the colors used etc. There are many interviews of the editor and technicians involved. Other than these, the commentary by coppola is good. But if you want to see something really good, you have to watch the documentary called "Hearts of Darkness: A filmmkaer's apocalypse" by his wife Eleanor Coppola. It is tough to find, as it is out of distribution now. Dossier along with the documentary (which is not included) pretty much covers everything you want to know about the movie and its making.
BTW those 50 min are edited footage. There is some talk of some more raw footage, but IIRC Coppola mentions that it was never intended to be released in that form.