Incidentally, the Sachs Aris freewheel you have should be spaced the same as, or damn well near enough the same as Shimano, but without the wave pattern cogs to aid shifting. Check out Sheldon: http://www.sheldonbrown.com/cribsheet-spacing.html
@roadrash started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
Incidentally, the Sachs Aris freewheel you have should be spaced the same as, or damn well near enough the same as Shimano, but without the wave pattern cogs to aid shifting. Check out Sheldon:
http://www.sheldonbrown.com/cribsheet-spacing.html