Recently this got posted at the WAF. Unfortunately, no one replied:
From some photos we can see at least three different types, two which are fastened only on the chest and shoulders and the third also fastened on the thighs.
1) Of this type there appears to be a kind of large front hook with large "D" rings, only around the chest
2) Of this type the hook is replaced by two leather straps, chest and shoulders
3) This is the mod. Heinecke, large front buckle and side buckles that go down the legs