well no wonder the thread disappeared while i was responding to it! confused the heck out of me. i was just mentioning that he post in a more appropriate sub forum.
back to the task at hand. since the reverse unit is not gear nor chain dependent, you need to verify the existing gears' tooth count prior to committing to a chain.
most of those either had 21/37 or 20/37 gears using a 72 link chain. if your tooth count doesnt match these numbers, post back and someone can verify chain length needed. be sure and include your existing gears' tooth count.