I'm was in a similar situation, ironically with a Bonti - running Paul comp. brakes and 700c wheels. My current 'off the shelf bodge'. I plan to rework the Mavic adapter to allow more clearance with CX tyres.
I have seen that and also this one:
http://www.biketrailershop.com/xtracycl ... -1600.html
I am thinking that the 700c version might be too high for 650b.
For those of you wondering, it rides like a fat tire cyclocross bike. Great feel, handles fine. I did have a little build up on the rear brake but nothing major. I will not be riding this in the mud.
1968 Schwinn Typhoon Deluxe
1984 Otis Guy
1990 Klein Rascal-Owned by Steve Miller
1990 Klein Attitude XT
2010 SSCXWC Raliegh Cross
2012 Black Cat Custom 29er SS