Thanks for the replies fellas.
Tim, I was thinking the same thing. Find a LHD car which has the steering box mounted to the inside of the frame, and that should work for me on the outside of the right frame.
Problem is the design of the boxes. Whilst the mounting is on the correct side, and the shaft and gear for the pitman are all facing the correct direction - they are on the wrong side of the box.
If you look at my image above, the steering rod is on the outside, and the pitman arm is on the inside closest to the frame. If I was to take a box from a '67 Camaro, the mounting holes are on the correct side, but the steering rod is on the inside whilst the pitman arm would be on the outside. So it won't work.
My RHD box:
67 Camaro box.
Problem with all other boxes I've seen from other manufacturers like Jeep etc, is they're all the same layout as the Camaro. Steering shaft inside, pitman outside - I need them reversed.