As I understand it it’s a pure BBY.
The original engine was BBY, so the wiring loom and ECU are BBY.
The ancillaries, and all parts that differ between AUA and BBY are from the original BBY.
If I understand correctly, the only AUA bit is the engine block/head, which is physically identical to the BBY version, so for all intents and purposes it’s a BBY.
I believe
@Azim also said that the engine has been running in its current setup too, though maybe I’m getting it confused with a different thread.