There can be a tremendous load on that fitting under heavy going... It will be difficult to make either of those types of fittings attached sufficiently strong.
We had a fitting that bolted to a long slug that slid into the sail track groove and locked in place. It was identical to the gooseneck pivot, so the rotation of the boom and the vang fitting matched perfectly.
This was on a 24 foot day racer.
Hopefully you can make sense of this... If the attachment bolts (which thread through the long slug) are long enough that they will pass through holes drilled in the back of the sail track as shown, the fitting will never move.
I believe this was a commercially available fitting, but we have had a machinist make one of these as well.