Originally Posted by surreal

my $.02-- 2mm offset won't matter for most "old mtn bikes", but might be an issue with a bike with very short chainstays. I wouldn't eff with chainring spacers unless your drivetrain ends up noisy/crunchy.

You'll likely want to leave the BB alone.

I'd strongly recommend getting a ss-specific chainring. They're not too expensive, and totally worth it. However, i'd run the set-up as-is before getting a singlespeed ring, just to see if you actually do have issues, and to make sure you like the gearing. If you think your gear inches are too steep or too short, you can go down or up a few teeth and upgrade to a SS ring at the same time.

Just an FYI-- singlespeed chainrings have no ramps or pins, which are found on multispeed systems b/c ramps and pins assist in shifting. In SS drivetrains, ramps and pins assist in dropping the chain-- not good. Most SS chainrings also have deeper teeth, which is a good thing for single speed.

-rob