you can swap bearings to 20mm, but the 20x47 are wider than the 25x47, so you have 2mm extra either side. speedo drive od is possibly the same.
the 41mm forks have 25mm holes at the bottom, so you could make a custom axle. might need to machine flats on the inside and outsides of the fork legs to make sure it's all square. or just pop it in and tighten the pinch bolts.