A yoke structure 6I (such as illustrated in FIG. 4) may be connected between pin 56 and a variety of points along the length of lever 59; and this is conveniently accomplished by providing spaced holes along the length of lever 59 and using a bolt and nut or other fastening means to affix bracket part of the yoke (see 44 of FIG. 4) at different points along the length of lever 59.