Anyway, you need a chest-height pack that wraps around the body to keep the camera tight? No problemI think. Most of these packs, of course, are made for cameras no larger than a typical 35mm; the Pentax 67II is much bigger than even a large 35mm SLR. However, Lowepro makes a fairly large chest-height pack called the Topload Zoom Pro AW that is 7.5 inches wide at the mouth and 6.5 inches deep. Your Pentax is about 7.2 inches wide and 5.9 inches tall (or deep), so it should just squeeze in there. The lens, attached to the camera, will fit fine. And there are plenty of little pockets for film and other small accessories. It's mostly weatherproof, well-padded, and equipped with a chest harnessshould be just the ticket. Cost is about $75.
After that, the list of things that will work gets very short. Your next best bet will be to get any ol' big lumbar pack, which can be reversed and worn on your front, albeit perhaps a little uncomfortably. Lowepro's Orion ($82), designed with cameras in mind, would work, as would a non-photo-oriented pack such as the big Mountainsmith Cairn ($90).
Good luck. And remember, negatives are forever!