You are right Otts is a good place for clutch repair and parts. I had mine done less than a year ago because the pressure plate broke an eye bolt and would not release. Really sucked since it was right before hunting season. They have told me 1"x10 spline clutch centers are no longer available and have not been for a long time. I think the 300 might be bigger but don't know without looking in a FSM. Otts takes about 20 minutes to drive to for me.
RR