It's a 61 FSR but what is interesting is the carb- the 61FSRs I have seen have 7D carbs (also shown in the OS pic that was linked on an earlier post), yours does not have a 7D. I had two 60 FSRs and they definitely had rear bearing issues, the 61FSR had a much larger rear bearing (which I believe is the same sixe as the 61SF). This should be a sweet-running engine for you, has a reputation as one of OS' best!