stationarily secured to the support bracket 154 to slide within the track 160 or rotatably supported thereby e g a ball bearing arrangement to reduce sliding friction with attention now to fig8 and 9 an embodiment of a top track 160 for use with the present invention may be seen as illustrated the top track 160 is a substantially longitudinal member extending between a first end 162 and a second end 164 a channel 166 is preferably defined by a channel sidewall 160 c extending between and including the first end 162 and the second end 164 the ends of the channel 166 are preferably open but may be capped after installation of the bearing 156 track mounting bracket 146 and or an end stop assembly 170 the end stop assembly 170 has a bottom plate 172 and a top plate 174 coupled to the bottom plate 172 in a spaced relationship by e g a threaded fastener 176 the end stop assembly 170 may be secured within the channel 166 at one of the track ends 162 164 or between one of the track ends 162 or 164 and the bearing 156 fig9 shows an interface between the pivot assembly 140 and the track.