Exactly the same problem I had, I bought a old regulator from a sedan? year unknown, but same size channel, still on it! cut it up, cut my rotten piece out, after measuring where tabs went, welded in new piece, grind down and took it to glass shop to have it installed in repaired channel!!!!

It is a common problem with bottom of the window tailgate tracks out of these old wagons.I have restored 2 Beaumont wagons and I think it took about a dozen tracks before I found 2 good tracks that I could actually use.Mine came out of cars from dry yards down in lower Colorado and New Mexico-anything i found close to us was always rotten.