the change over was in 93, wvhich means that 66% of the NSR's probably have the non MC28 type pump. If you can get an MC21 pump with the oil feed, you can use it, but you have a better chance of not getting one then you do.

The other option is to block off the oil galley in the engine case, and go with the MC21 pump that just feeds the carbs.

Either way, you best off just looking for an MC28 pump as trying to explain to someone who's selling a used MC21 pump what to look for could be hit and miss.