My 76 D100 was an HD package. Had a 9-1/4 and a 318 with a 360 4 barrel intake. Ive read supporting information saying HD's came with a 360 4 barrel intake but nothing that is straight from Chrysler Corp. Just internet chatter. It was a Cal Trans truck with an Adventurer package too. I was told it would have been a supervisors truck being a short bed and the fact that it is in better than "work truck" shape.