I've been trawling the 'net for info over the last few days and I just can't find exactly what I'm looking for.

As there are forty thousand versions of the BW diff are the casings stamped to indicate their characteristics or what vehicle they were in? I wanna know what type of diff mine is (all I know is R31), regarding spline, gears, etc, without pulling it apart.

is it r31 skyline or pintara?

if skyline then its BW78 with 28 spline axles and either 3.7: or 3.9:1 center, most likely 3.9:1

if pintara then its 25 spline with 4.11:1 gears

housings are the same as well as brakes

similar housings came in Vk series 2 or 3 till vs commodores(live axle of course)
Vn onwatrds were all 28 spline and use the same centres as skyline, gears are also interchangable

Not sure if it's Pintara or Skyline. I'll test the diff gearing then and see which one it is.

Thanks for the help.

There should be a ratio tag attached to one of the lid bolts. It will either say 3.89:1, 3.7:1 or 4.11:1 if it hasn't been messed with.

Sweet, much easier than rolling the car.