Identification locations:
- Axle housing - number faces chassis.
- Differential cover plate flange tag - Can reference this number with Holden.
- Different centre carrier housing.
- Bevel gear.
- Pinion gear.
You will most likely have the BW 75 Series open centre differential with a 7.5in crownwheel and 3.08:1 ratio gear set.
My ute was a stuff around when I did some modifications. I have:
- BW 75 Series axle housing
- BW 78 Series 28 spline axle shafts
- BW 78 Series LSD differential centre.
- BW 75 Series 3.45:1 gear ratio with shot peened gears.
Differential centres are interchangable but you match the axle shafts to the centres, or change the axle spider gears. Also you can't fit BW 78 gear sets in BW 75 Series axle housings as the bevel gear is too large, being 7.8in instead of the usual 7.5in. They will fit though, only if you machine the rear pinion bearing cup surface down by approx 3mm. You can however, install BW 75 Series gear sets into a BW 78 axle housing as long as you add approx 3mm of shims to the rear pinion bearing cup surface.
BTR Engineering and Borg Warner manufactured the live axle setup for various makes and models.
I hope this answers your questions, feel free to ask more.