The Godfather Epic is the chronological version of Parts I and II released on VHS/laserdisc. It has more footage than the original two films. The Godfather Saga (aka: "Godfather: A Novel for Television" - not available for purchase on VHS/laserdisc) is the TV version of The Epic, but it has much more footage than the Godfather Epic. Most of this extra footage ended up in The Godfather Trilogy box set (Re-released in 1997), which is the chronological version of all three films, available on video/laserdisc. The Trilogy set is the one you should get if you want the most available footage. The Godfather Collection is simply the three original films in a box - no added footage, and not in chronological order, but remastered/widescreen in 1997 and later released in a similar box set on DVD in 2001.
Hopefully this helps anyone who decides to take up the project for us and needs to know what to look for on Ebay. Basically any of the extended versions wouldn't be complete, since each has scenes not in the other versions while at the same time missing some stuff that's included in the other versions. If anyone was to do an ultimate fan edit they'd need all the versions to combine all available scenes together. Personally I'd just be happy with a DVD of the Epic/Saga version since GF3 barely has anything different.