I went through both Riesner's script and the first draft of Puzo and Coppola.
I like Riesner's ideas, but his storytelling is a little sloppy.
And the first draft of the 1989 screenplay of Puzo and Coppola may be even better than the final version.
It's more focussed on the mafia and it's world, and far less on Michael's quest for redemption. His character in this first draft is more like the Michael we know from the first two films.
Only, I didn't like it's ending and I'm somewhat indifferent about some events.
You can read the screenplay here:
http://www.awesomefilm.com/script/godfather3.pdfHowever, I must add that both screenplays have Lampone as a character, which I think is impossible.
If he somehow survived the shoot-out, there's simply no way he would have been at large after this. He killed an important person in front of the FBI and would therefore most likely been sent to prison for life without parole.
Also, in the first draft, Willie Cicci returns as a character, which is very hard to believe. Michael would have never forgave him after Cicci had testified against him. He would have been a dead man walking.
I'm really wondering why Puzo and Coppola came up with this in the first place.