Thats what I was wondering too,I found this on Sheldon Browns site

ld three-speeds can also make quite satisfactory fixed gear bikes, particularly English ones. The rear triangle is already just about perfect for a track hub, they usually have 110 mm spacing. The better English 3-speeds had pretty nice riding frames, and can be very pleasant bikes for not a lot of money.
If you replace the 590 mm (26 x 1 3/8") wheels with 622 (700C) wheels, the bottom bracket gets raised a useful amount, providing good ground clearance. Using the larger wheels also allows you to install a better, shorter-reach brake caliper.