I use conventional turnbuckles and chains on my camper. The chain is attached to the Torklift by a "quick link." Neither the nut end nor the threaded end will pass through the hole in the Torklift plate, but the main cross section of the link slid quite handily through that slot you are complaining about, allowing me to attach the chain to the Torklift bracket.
There is enough "meat" around the hole that the slot isn't going to significantly compromise strength. The rest of the bracket will bend long before that fails.
