further pivot pin 151 b moves towards angle bracket support leg base 124 b and pivot pin socket 133 b in response to pivot pin actuator 150 moving to the extended condition hence pivot pins 151 a and 151 b are repeatably moveable towards and away from angle bracket support leg bases 124 a and 124 b in response to moving pivot pin actuator 150 between extended and retracted conditions respectively further pivot pins 151 a and 151 b are repeatably moveable towards and away from pivot pin sockets 133 b and 133 b in response to moving pivot pin actuator 150 between extended and retracted conditions respectively fig6 a is a sectional front view taken along a cut line 6 a 6 a of fig3 a of opposed tower brackets 116 a and 116 b and tower interface assembly 118 in a region 114 of fig3 b in this embodiment mounting blocks 146 a and 146 b are mounted to opposed tower brackets 116 a and 116 b respectively mounting block 146 a includes a mounting block opening 147 a which is aligned with tower bracket intermediate opening 191 a further mounting block 146 b includes a mounting block opening 147 b which is aligned with tower bracket intermediate opening 191 b mounting blocks 146 a and 146 b are for holding angle pin actuator 140 to opposed tower brackets 116 a and 116 b as will be discussed in more detail below angle pin actuator 140 extends through mounting block openings 147 a and 147 b in this way angle pin actuator.