78 it sound like the tags are on the wrong side and you say that the passengers side is dated 05/78 if it's a hj it must be 5/76 kg are right for v8 sandman did you get tyre placard ,what about full length head lining , courtesy lights m41 is turbo 400 which I think is ok for hj but maybe reasonable rare . I think your p or r would be F for 1976 .so I think you should do some more investigation and measure the width side rail for the the hood linning this may also help you