In order to tell the difference between the Series 1 and Series 2 engines you can look at their CAS Housing. The Series 1 RB25DET engine will have a Metal CAS Housing While the Series 2 RB25DET engine will have a plastic CAS Housing
No. Most aftermarket hubs will not support the ABS system in a Nissan S13 240SX due to a lack of ABS rings. Because the ring is factory pressed in and are extremely fragile it is not possible to transfer them over from an oem unit either. If one wants to keep their OEM ABS system the best route to swap in 5 lug hub components and retain the ABS is to purchase Nissan S14 5 Lug Hubs and the corresponding knuckles (S14 OEM Front Knuckles - RH_40014-70T10 & LH_40015-70T10). Doing this ensures the proper functioning of the ABS.