Some pics and updated info. I've since bought an RNU12 bluebird instead of performing this swap. Here are some pics that will shed more light on the swap for anyone wanting to do it.
The crossmember from the U12 would have to be removed and replaced with mounts used by the RNU12. Notice the missing crossmember on the bluebird running from radiator to firewall. This cross member on the U12 holds the left hand engine mount (radiator mount) and the right hand mount (firewall mount). On the bluebird these mounts are totally differant, especially the right hand mount on the firewall.
Notice the big 'pipe' on the bluebird running across the front of the car. This is square on the U12. Another differance.
The front engine mount is exactly the same on each car.
The rear engine mount is also exactly the same. This is a shot of the bluebirds mount (under the battery tray).
The left hand mount that sits infront of the radiator (its the same on auto and manual bluebirds). Auto CA20E & KA24E powered U12's don't have a mount here (manual's do). Its differant to the manual mounts on the aussie delivered cars though. To perform a swap, this would have to be changed, it mounts onto the 'pipe' like cross member that runs along the front of the bluebird. On the manual CA20E's and KA24E's this mount is connected to the cross member that runs from radiator to firewall, which is missing on the bluebird.
The major differance between the two motors and their mounts. The bluebirds right hand engine mount (firewall mount) is located much higher up than the aussie cars. It does not bolt onto the crossmember as discussed earlier, but bolts onto a bracket that is welded directly onto the firewall. This bracket does not exists on the CA20E powered U12's. It would have to be welded on, or the bluebird mount adapted to suit the CA20E's existing mount location.
You can see the brown mount on the CA20E car sits right down next to the exhausts flex pipe. The bluebirds mount sits much higher up, about half way up the firewall.
And one final pic of the two engine bays just for kicks.