anyone have a picture of this? trying to figure out how this would look

The single Minoura saddle mount cage holders will not work on a Brooks Swift. The rails are too far apart to get a good grip with the holder. Don't think it would work on the B17 either, but I am not positive (never tried, just looked at a B17 at my LBS, and the rail placement seemed to be the same). This is the one I have:
https://www.google.com/products/catal...d=0CF0Q8wIwBA#

B17 is the same- too wide for that type of mount.

If you are considering attaching water bottle cages on the back of your saddle, looks are the last thing you should be concerned with. I mean, you put a vintage touring saddle on what I assume is either a track, tarck, or sweet fixie bike and you are going to add some Triathlon tech water bottle cages to it. It's just gonna be weird. But if it helps you ride longer, faster, and harder, then more power to you. Don't concern yourself with looks. Stay hydrated.

Wear a beer helmet.

I had a profile aqua rack on a swallow that worked

This Profile Design mounts on the seatpost;