I really don't understand why people are having issues with chain length. If it's ordinary straight or twisted link chain you pick the link that gives the length you need, put a shackle through that, and let the remaining part hang if it's short, or use some safety wire or whatever you have to tie it out of the way if it's long enough to drag.
As for the shackle coming loose, use a screw-pin shackle and position it so that the screw goes in from above and gravity will be your friend. If you don't trust gravity, a little piece of lockwire through the hole in the pin and around the shackle body will be your friend. Or get a shackle that uses a cotter pin to safety the screw (McMaster has those).