Maybe you're just consumed with the novelty of the idea... and I don't blame you, considering how OMGAWESUM people go over the RB26.
But in reality, save certain situations, the 2JZ is the superior engine. Its lighter (yes, lighter), much cheaper to mod, and the torque band blows the RB away.
Even the GT-R guys want 2JZs, its that good.
But the reality of an RB in an A70 is a bad one; heavy motor in a portly chassis, with less displacement to shove it all around. There are literally no pros to doing this (other than a weak "it would be kewl") and a whole list of cons.