Dr. Phan is chosen as Prime Minister for South Vietnam rather than Mr. Diem. A slew of butterflies ensure to maintain a surviving South Vietnamese state.
So far, the timeline has had two different versions:
a.) The original, Mk I version, now abandoned. It can be read here.
b.) The current, Mk II version, which you can read here. This version includes the creation of a stronger non-communist political structure within Southern Vietnam.
The characters and overall themes have been incorporated into Twelve Minutes to Midnight.