Mitch, here's an option for you -- get hold of a 105 mm Agnar from somewhere (cheap -- comes on Agfa Billy or Ansco Viking cameras, most of which have bad bellows by this point), and mount it on your Crown -- this part shouldn't cost as much as $25 plus shipping. Then, either convert to a Graflok back (might run to $100 or so) and use the Shen Hao 6x12 roll holder, or mask down regular 4x5 film to the 6x12 format.

Set the Agnar's built-in focus to infinity and stop it down to f/22 or smaller, and it'll easily cover the 6x12 format; if you set infinity focus carefully on the ground glass and then lock the bed, you can focus with the front element just as you would have on the original Billy, or you can leave the lens set at infinity and focus on the ground glass as you normally would with an odd length lens on your Crown. The masked 4x5 is going to be the *cheapest* way to get semi-pano without spending a mint -- a 105 mm on 6x12 will give about 100 degrees corner to corner, and you could spend as little as $25 (plus sacrifice of a dark slide to make a mask). In fact, I might have to try this with my Speed...