Back before the Hill brothers came out with their own internal frame packs. They used to modify existing external frames (Dana, Lowe, Kifaru, and Alice frames) with their yoke harness and belt. IMHO, the yoke harness is the most comfortable I've used. Another benefit is the harness can be taken off the Alice frame and used with a jungle belt setup if so desired.
Here are a couple threads started by "Alpendrms" K. Galbraith, who served in the 10th S.F Group and is a brand ambassador for HPG.