Alffie
Using the AU diff, I would suggest using a KAAZ centre in them, they are tough as nails and won't break, that is mnot to say that the axles wont give way. we have put them in cars with 350 to 370 rwkw, mostly VZ commodores which are both charged and normally aspirated. see
www.kaazusa.com (cant get the link to work.)
I noticed the LS7 in there, looks great, are you running the dry sump combo? How are you going to get it through rego, the exhaust manifolds are a dead give away!. That engine is a work of art and with 427 cubes it has a nice touch to it..
Steve