M_Boats: M15 turnbuckles

My 1981 M15 has turnbuckles that look like parts from an Erector set. (A series of 12 holes for inserting the clevis pins) None of the settings result in appropriate shroud tension. Is there another type of tension device M15 owners are using? I am unable to find a jaw-to-jaw turnbuckle short enough to do the job. Appreciate your help. Mike W M15 #139