yes its classed as a defect if you dont have an engineers cert which is very difficult to get, ive been researching this for a little while and spoke to a guy who has built a pioneer demo vehicle which just happened to be an r34 gt-t with vert doors.
they were very well done, i cant remember where he said they were done, i think it was something along the lines of K&M motor trimming on the goldcoast, and they are engineer certified, he used a kit that is a direct bolt on for a 350z and they had to be modified slightly to fit the 34, the doors are also weighted to allow you to leave them open at any angle in their range and to close them its as simple as pushing them all the way down and pull it in,
they cost him between $4-5000 but they were very well done, and closed perfectly, and since he had the engineers cert the werent illegal...
hope this helps
Steve
oh i jus found their site, its Kam motor trimming, and they are in burleigh on the gold coast,
Kam motor trimming link