Wrong - you can convert a non-lockup to lockup all day long. Case was never an issue. Nothing in the case is different. There was a slight "machining" clearance cut - but the casting is no different from previous years. And i believe this slight machining change was needed only for the early valve bodies that used the lockup module - the later electric lockups with the electric solenoid don't need that cut. As for dismal failures of the 78 lockup in big block applications - i am not aware of any mechanical failures - they were customer unacceptable because of the drone noise due to low vehicle speed lockup at low engine speed - causing a drone noise.