The 2003-on 9-3 has nothing in common with the older 9-3 (except the 2.2 TiD which was carried over) - the platform was entirely new.
The bulkhead issue is not GM900/OG9-3 alone it's a GM2900 issue that affected Vectra A/Cavalier Mk3 and Calibra too. The new 9-3 was made on the Epsilon platform with Vectra C.