I think I know what you're getting at. Are you looking at the SC 1.5 with the centered cross piece with that stamped eye? If so, the twist link is connected directly to the base, without a swivel point. If you want to change the chain you can either cut off the existing chain, and leave the 1 link section that is fixed to the trap, add a swivel and then attach the chain. Another option is to remove the chain all together and drill out through the stamped ring and favoring the frame side. This will allow a quick link to fit through, and you can do what ever you want with the rest. A "J" hook requires a ton of material to be taken off. A "S" hook will fit through, but I don't see any advantage over leaving the 1 section of twist link instead. The quick link with a swivel attached directly to it will lay flat, and have a closer swivel point to the trap. Make sure to weld the jaw ends, or bend them up if you want a shot at holding a yote in a SC 1.5
I hope this is what you meant.