Just how brave are ya, my man? Borg Warner/BTR had the Oz maket cornered for 78 -series diffs. Some were four pinion, some had crushable spacers to set preload.
So long as the housing is compatable you can choose from the following:-
4.11:1 Nissan Pintara (AUS) Had 4 pot engine
3.899:1 Holden Commodore 4 (NZ ONLY)/Some Nissan Skylines(AUS)
3.7:1 Ford Cortina 4 after 1972 and before 1981, Nissan Skylines
3.5:1 Ford, Valiant Utes, Charger E49
3.45:1 Commodore VL on, Falcon XR L6/V8
3.27:1 D option Charger, Commodore VP V6 option
3.23:1 3.3 Falcons, Falcon Utes, Valiants,Centura, P76
3.08:1 EB Falcon, VL on Commodres
2.92:1 Ford, Valiant, Cortina,Centura,P76
2.77:1 Ford,Valiant, Cortina,Centura,P76
2.53:1 Ford 6 (option on XD, XE apparently)
Some of these are 7 5/8", others are 7 7/8". Some changes were made which stops some combo's but I don't know which ones. However, I'd go for 4.11:1 ex Pintara. This will make open road cruising feel like your in second, not top, and will ruin all economy over 85 km/h. If you have tyres 650mm tall unloaded (like a 245/60/14), it will give 29.3 km/h for every 1000rpm. On the open road, 3800 rpm will give 111 km/h. Maximum top spped will be 141 km/h at 4800 rpm. At 60 km/h in first, it will be 200 rpm into the red at 4800 rpm. You'll note the rev limit was 4500 rpm for a 4.1 XF. This means that a Rice Burner will see your nose rise, and the engine scream like a boomber before the rear axle transfers the grunt to the tyres.
If you are running 265/50/14's, this ratio will be far too low, and 3.7:1 Cortina 4 will be better. I think the Cortina 4's had pinions which had a crushable spacer, and you may have to get a crushable spacer fitted to it. The Skyline one should fit too. It will have similar gearing to the 4.11:1 with 600 mm tall tyres. Oh, the speedo will be out, and don't blame me if you get arrested for getting booked Assult With a Deadly Weapon. Six cylinder pistons through the bonnet can kill passers by!