You will need a certificate for any change in engine make
and you are right the XR6T is hard to beat in Oz its mad.
You can always put a datsun logo on the rocker cover
or Henry loves old Dattos )
 
since you will need an engineering certificate for the Barra
might as well go tilt tray or gonna need a big ramp unless
you can use air bag rear so the b20 wont complain going up.
 
Im sure the diff will handle anything as they are a big mudda.
Looking forward to this crazy build.
 
You can also post on Ratsun for awesome tips as well
 
They would probably say put this donk in the back
with an auto and 4 pipes coming out each side
like a 60s rail dragster



 
but even an RB30ET has forged crank and rods are cheap
you can pick one up for beer and build it up yourself with
cheap parts and looks quite good and simpler for an old truck
Barra has cast crank and bigger form factor