Heres a link to a site with details on the Alfa diff tht I have been using from a late eighties Alfa Berlina 4,3:1 ratio. You also get em in 4,11 & 4,54 & 3,9. Check the local Alfa Club, maybe there are some lying about.
http://www.alfamilano.com/articles/lsd/alfa_lsd_rebuild.html
By the way, the diff housing/casing is partly aluminium but I can assure you the bearing carriers are definitely not. From all reports, they seem to handle up to 500Nm of wheel torque before they pop - remember its torque that kills drivetrain parts, not kilowatts.

not sure how common those particular diffs are in austrailia, but it would be an excellent choice for a LSD upgrade! D had a pic that compared the alfa diff to the H165 and there isn't much difference in width.