I got a pair of the Yuketen chukkas earlier this year and was told (by Meg Co.) they were made with a "C-width last." For me they fit perfectly. They fit much better than my Quoddy bluchers, which have stretched out (it's okay for now, though -- I just keep pulling those laces tighter & tighter). I was also told (by Meg Co.) that Yuketen was switching to a wider last for their shoes & boots. .
Btw the Yuketen mocs I tried in different locations in JP (boat shoes and ranger mocs) were narrower than EU/US sized yuketens. I wear a EU/US 9.5-10 and the JP 10s were definitely too small. It might not apply to all styles though.
Saw a pair of Yuketen's at the saks sale about a week or so ago. They were black 8" crepe vibram sole similar to a guide boot. They were on sale for $230, but looked really great. Dam shame they were a size too big.