Here's a photo of the card.
http://antiqueradio.org/art/temp/BTCard.jpg
Peering back at your photo, it looks like I have an extra set of DIP switches. I believe the 550 in the model number means that mine can reach higher frequencies than the 450. If I were designing this stuff, I'd make the two models compatible so that the same settings would work for lower frequencies that they share. But maybe that's expecting too much.
I haven't tried looking for an owner's manual. Some companies put all of their manuals online.
Phil