MadTimo,
There are no external markings that I've noticed. All you can do is identify the cars that had the ratio you want, then find said car at a wreckers and hope the diff head is still there. Then its just a case of pulling the head out, once the head is out , the ratio is stamped in the outer edge of the crown wheel and looks something like "HC 39:8 ????" - 39 is the number of teeth on the c/w & 8 is the teeth on the pinion, so 39 divided by 8 equals 4.875!

According to the diff tech section on here

Brent, how do you know what to look for when finding a 3.9 or 3.7 H165?
Are there any markings on the diff that identify what it is?

thanks well to answer ur question , too far away im in sydney australia hehe

neither the coupe or the sedan will fit - they run the smaller diff, the H145.

You need to find a car that run the H165 diff and try to find one with a 3.9 or 3.7 ratio.
- some of the ealry stanza's & bluebirds e.t.c.

Where abouts are you?

thanks mate thats helped us out alot would u be able to tell me if with the coupe or sedan diff whether i can just change the inside or all of it, mines got a five speed sunny gearbox if that helps u at all.

Using a 3.9 (as in the coupe or sedan) will let you go faster (higher kph) for a given engine RPM. It will extend the speed range for each gear.

On the other hand, there will be less rear wheel torque.

So you'll have less power, but your engine will last longer not being revved up so high all the time. You'll also have a more driveable comfortable ute I would guess.

well you probably have the H165 and it should have the 4.1 ratio in it.

Where are you? I have a 3.9 if you want to give it ago to see what its like.

howz it goin, ive just bought my self a sweet 1200 ute and ive noticed that it seems to rev out first and second gears real quick but doesnt go bery far. i am looking into getting a new diff so it will go a bit further in firts and second. does anyone know wat diff i could use to get this effect?