The German made Sun-Sniper meets your requirements for steel anti-theft cable and across the chest. (it says "Home" but its Sun-Sniper.de)
Home
I use one and its well made and comfortable. Also comes in multi-camera configurations. However it normally screws into either the tripod mount on the camera or the lens. You would have to attach your own strap to the normal neck-strap loops and forgo the screw, or if your primary lens has a mount that rotates, screw into that with the mount rotated so the camera sits flat. I just tried it for fun and it seemed ok. As always, YMMV. Good luck.