That Kifaru rig wouldn't work for me at all and I can see how it would be a real pain with a long heavy gun.
The thing that strikes me about it right off is that if you should trip/stumble and fall forward your muzzle is heading straight for the dirt.
Having the muzzle out in front of my face would just flat drive me nuts as well obscuring my vision.
I think I'd much prefer the Eberlestock
system over that either with the side scabbard or scabbard centered on your back inside the pack.