Hi Alffie,
I'm the one that did the Commodore diff conversion. Who mentioned it to you?
The AU ford diff is a BTR-75 center which has a 7.5" crown wheel. At the time when I was building my rear end there were only 2 ratios available for it. 3.23:1 and 3.54:1 I wanted 3.7:1 or 3.9:1 so I bought a BTR-80 center from a VU GTS Commodore. This center comes equipped with a stronger 8" crown wheel and 3.9:1 gears and a Hydratrak LSD center.
The BTR-75 and BTR-80 share tha same back cover bolt pattern. I used the Ford AU back cover on the Holden center so I retained the standard rear chassis mounts. I machined the back cover to add a fill bung as the Commodore housing has the fill plug in the back cover where the for has the fill plug in the housing. I also welded a tube through the rear cross member so I could get to the fill plug.
I cut and boxed the cross member in front of the diff as the front mounts on the diff housing hit on it. I then fabricated and welded in a new front moung to suit the Commodore housing.
I made up some nolathane front mounts for the diff but If I did it again I'd probably solid mount it as the extra vibration would probably go un noticed with side pipes and everything else going on.
I'm using the Commodore axles as well. I never liked the Ford axle design since to remove an axle was a major pain in the arse requiring stripping down most of the rear end. I can undo the 6 bolts one each end of the axle and drop it out almost without turning a bolt on the rear suspesion.
I also plan on fabricating some tubular molly upper and lower control arms that will be 2" narrower each side. The commodore axle setup makes life easy for shortening the rear with the way I've done the drive flanges at the wheel hubs (unfotunately I don't have any pictures of them).
The 6 ball CVs seem to be a bit stronger than the 3 roller style used by the Falcon (Going by the punishment the Commodore guys dish out). There are also aftermarket CVs available in this pattern that are much stronger. The standard Commodore axles are also 2mm larger in diameter than the Ford units.
Cheers