They're rivets. And yeah, I was hoping to do some heavy weather sailing, "break" the new boat in, so to speak. But not the sort of sailing where the vang tears the whole plate loose from the mast!
So I like your advice of moving the plate up and finding something stronger to attach it. I could be wrong, but to me rivets don't seem strong at all. Plus there's the problem of not having a rivet gun in my arsenal.