the "you don't know the truth obi wan killed your father" dialogue was the fake dialogue everyone had except for like 5 people who knew the real lines.
Even Dave Prowse on set recorded dialogue was that obi wan killed Lukes father. And it was Prowse who supposedly Leaked that to the British Tabloids. Lucas was so furious that when it came to filming the prequels Prowse was not welcomed back, and the rest is history we got Hayden Vader.