I'd still ring bara, he should be able to advise on anything diff related and everytime I've contacted him I've been impressed with his knowledge.
Personally I'd be looking for an atb type diff for a road car, or pretty much any fwd car tbh.
Good luck with your search, if you don't turn up a suitable solution please let me know, I am local to bara and I have a spare box for a mock up. Seems a common area that's lacking options for the beta.
Cheers
Dan