Here's the build thread.
https://motorbicycling.com/threads/cannonballs-abbynormal-3speed.58233/page-2#post-600295
I have been watching ebay for these 3 speed fixed gear hubs, but considering the prices, it makes more sense to convert an old aw hub or miniaturize a basic dog box transmission.
Basic dog box, although the clutch be simplified:
http://www.thepixelpump.com/widdershins/how-to-2speed-transmission.php
A basic description on the 2 fixed speed conversion from James Fairweather sounds a lot easier than machining the bearing cup and planet cage, but that's still an option.
how to convert a Sturmey-Archer AW three-speed hub Into a two-speed fixed gear
www.sheldonbrown.com