It might be best to talk to the officer at the Sydney Datsun Club about this. At the Sydney Datsun day there were a few cars on Historic plates that I couldn't understand. These were probably the Modified Historic Plates. If an engineers report is needed, they might have a preferred engineer. A friend has a Hillman Minx on Historic plates, he had to take the mags off it to qualify for the plate. I've got 2 Sunny's I know will need engineering when I reregister them, I'm hoping to get them on Modified Historic plates.