I believe the standard gearing was 20/39. It's pretty common to simply drop a tooth on the top gear to achieve a little more bottom end pull. If you go that route, I would dig into the chaincase first to be sure you have the correct gear combo, and thus get the right gear when purchasing the new one.
The correct gear combo that it's presumed is in your sled. According to what I looked at, your sled should have a 20/39 combo. Somebody may have been in the chaincase before and altered the stock setup. Open it up and see what you have for gears before regearing it, if that's what you are going to do. That way you know exactly what gears you have, and what you will need when regearing.
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