Hey man, i don't know if its to late, but i found this on a different website:
https://www.auto-data.net/en/bmw-3-s...eptronic-42234.
Wich basicly says it is a B48B20A, wich is the same engine as in the 330I.
The problem if you want to tune the car is that the DME is locked, so i think you need to send the ECU to someone that can unlock it.