Spec RVR 1991 - 1997 Engine & Model Option 
File
Spec Rvr Sport Gear.DocAuto Body Modification Ratio
N43W UPF5, UPF6, FRF2, FP6 3307
N44W UPQ1, FPQ1 3307
N48W UPF4, FPF3 3307
N21W UPF5, UPF6, FPF2, FNF 3307
N21WG FMF 3307
N23W WNQ, LNQ 3545
FN6 3307
N23WG WMQ, LMQ 3545
FM6 3307
FM61 3307
N28W UPF4, FPF3 3307
N28WG WMF, LMF 3545
first digit of the body means the model and drive:
1.3 - front-wheel drive, 2.4-full
1.2 - PBP, 3.4 - Scharioth
the second number refers to the type of engine:
1 - 4G93 (petrol)
3 - 4G63 (petrol)
4 - 4G64 (petrol)
8 - 4D68 (diesel)
So 4G63 engines were both single-shaft and twin-shaft. also are turbocharged.
