Heres an update on what is working for me. A friend had a stainless slug custom made years ago when he had the same situation. He gave me the slug after no longer needing it, he said it cost him $30 to have it made. The slug is 3/4" diameter, with the bottom third ground flat. It fits perfectly inside the track, and almost completely fills the track from side to side, but still has plenty of room to move. There's no way this thing is coming out. I've used it twice in strong winds, and once where we sailed with reefed main and no jib and still moved at 6.5 kts. I kept my eye on the slug and it wasn't pulling up or bending the slot. It doesn't appear that I'll need riveted plates, or velcro straps. The bigger slug seems to have done the trick.
