What if you guys drilled a hole through the higher part of a beam, joist ,bearer whatever your country calls it and drop a solid metal rod through the beam itself and hang it off that, even span two beams with a metal rod, buy it from a scrap yard thats never coming loose.

Or are you mounting a swivel device as well?
We've even wrapped 1/4 inch fenceing wire around the whole beam a few times and tied one into the bottom of the loops, fuk screws they are not going to cut it. Rope right around the beam even. Use a large U screw bolt to connect the chains to the rope or the chains to the wire. Going up through a beam vetrically I would car bog an expanding bolt into a hole, tighten as much as possible, you can even get them with large metal circles welded to the nut that opens the claws on the bolt.