As originally rigged (roller reefing, round boom), the M281 had no vang. My boat came with a cast aluminum horseshoe with two urethane?
bumpers that could be slipped along the boom and a
line tied to it to serve as a temporary vang or preventer. I've never used it.
I do
rig a preventer by tying a
line around the boom at about the midpoint (I slip the
line between the boom and the boltrope of the sail) and leading it to a stanchion base. However, as I've rigged it, it's not a vary efficient vang.
On my M281, the downhaul is a short
line (about 3' long) fastened to an eye on the bottom of the gooseneck car and made off directly to a
cleat on the back of the mast. There is no separate hardware. Even with this setup, I find it fairly easy to overtension the luff of the sail.
My boat has never been rigged with a cunningham. Since the gooseneck slides up and down, the downhaul serves the purpose. If you are racing, it might be another story.
I can imagine numerous upgrades to this setup that might have been made over the years, but they would be individual to each boat.
I've gone over my archives, but I've never taken a clear photograph of the gooseneck area.
I wish I could be more help, but I think you're going to have to use your imagination and examine other boats in your marina to fix this one.
Rich