I am going to give the B135 a try on my Kona Humu cruiser along with more upright position handlebars than it currently has. I found a U.S. dealer who lists it for close to the British price including shipment from Britain.

Per what I have read the seat sandwich can even be modified to work with some dual bolt seatposts if you have access to a drill press or files. There used to be a version available with a much larger central hole that worked w/o modification.