I just built a new front wheel for my Twenty. Mine already had 406 wheels with the ultra-crappy brakes. I had to spread the fork to accommodate the standard length axle. I also had to spread the front dropouts to accommodate the standard diameter axle!

I used a Sturmey Archer drum brake hub, which has a very good brake. It doesn't care about rain or snow, and it will probably prove to be ultra-low maintenance.