Although it may not be historically altogether true I do like the premise of Vincent having to fight off the Russian mob.

I also see the story as having a much darker tone. Personally i think I would involve the Corleones in the drugs-for-guns Oliver North stuff. Have the family funding the anti-Sandista regimes in exchange for cocaine which is shipped to Sicily where it fethces a better price in the european markets whereas herion made more money in the US. The Pizza connection stuff would be a part of it as well as trying to take over Atlantic City while pushing that family out. I wouldnt have the family triumph in the end though. Vincent would either be given a death sentence and executed or die by being poisined in prison because of what he knows (govt dirty secrets). I would try to find a way to tie in the Rizzi's rebeling similar to the Bonanno capos when Joe Masseria had to take out 3 at the same time. I would have Vincent also becoming extremely paranoid and trying to take out govt rats similar to what brought about Gaspipe Casso's downfall.