diff ratios
Looking at the Nissan electronic parts catalogue, there is a bewildering array of different gearboxes, and internal gearbox parts. The numbers RS5F41A refer to the 5 speed box and RN4F40A the 4 speed. The internal ratios could be anything though. They mix and match depending on the year and engine.
Luckily there appears to be only four part numbers for crown wheels for the manual gearboxes. What this means is that there are only actually three final drive ratios fitted to normal K10 gearboxes.
81/20 (4.05)
80/21 (3.81)
79/22 (3.59)
All 4 speed boxes are 3.81.
All 82-85, 5 speed are 3.59.
All 85-87, 5 speed are 3.81
87 onward, 5 speed MA10 are 4.05.
88 onward, 5 speed MA12 are 3.81
These are the parts available anyway, whether these combinations were actually sold in the UK is a different question. The actual gear ratios aren’t listed I’m afraid so I can’t tell you those.
I hope thats of some use? I guess you are looking for the lowest ratio (4.05) found in the later 5speed MA10's?
Craig