Ooh -- that's great information! That ought to be exactly what I need. Here's what I got from the company tonight:
The metal pieces go with the x-sill. They fit or are welded to the frame and the x-sill goes on them.
Can't make out the rubber piece from the photo, sorry.
I'm really not sure what they were talking about with regard to the metal pieces. Can anyone enlighten me? What's the x-sill?
And I was slightly surprised that even the vendor didn't know what the rubber was for. Oh, well. Gotta track down a Steele catalog....