Have never seen a tack fitting splayed out like that, and can't figure out why it would be like that or how it would work, so I understand Nolatom's concern. Further reading about the J/24 class, however, mentions that the mainsails have "floating tacks", and one article J 24 Tuning Guide
(dated 2002, by Shore Sails) suggests cutting the tangs off entirely, since "they're not needed". I cannot find any pictures of it, but the best advice might be to check the J/24 association website for the latest information on how the boat is rigged.
The Cunningham was invented because sails can't be stretched beyond the black bands on the mast. (This is so that all the sails in one class are the same size.) In light air, it pays to have fuller sails, as big as is allowed. If the wind increases and your sail is already pulled out as far as the black bands allow, how do you make the sail flatter (for improved performance in the higher wind) without pulling the downhaul beyond the bottom band? Enter the cunningham. It is essentially an extra-high tack grommet, invented by America's Cup helmsman Briggs Cunningham, which enables you to pull down on the main luff without making the boom go lower (beyond the black band.) Any sort of multiple purchase setup will work. You could attach a block to one of your tack-fitting holes (since you don't need the tack fitting...) and attach a line to the tack fitting on the other side. Run the line up through the cunningham hole, through the block, and back through the cunningham hole. You can then tie it off to the tack fitting somehow, or end it in some other convenient place. Harken will sell you blocks to make the thing 40:1 if you want it, but more than 4:1 is probably overkill.