pairs of forward and rear sprockets 21 and 22 to mount spaced parallel first and second continuous conveyor chain members 19 and 20 operatively associated with the forward and rear axles for rotation of the sprockets by rotation of the forward axle 16 by use of a reversible drive motor 52 utilizing a drive gear or chain 53 to rotate the forward axle 16 and the associated first and second chain members 19 and 20 cross braces 18 are utilized to mount the guide rails 14 and 15 to the tractor framework 13 in a spaced relationship above the tractor framework to slidingly receive the trailer organization 12 thereon reciprocatably mounted upon the 34 c 34 shaped guide rails 14 and 15 is a rectangular trailer carriage 23 extending laterally beyond the sides of the guide rails 14 and 15 mounting a wheeled assembly to enable reciprocation thereon the trailer carriage 23 is secured to each of the first and second chain members 19 and 20 a connector link 24 pivotally mounts the trailer carriage 23 upon the chain members at a position forwardly of and adjacent a rear longitudinal edge of the trailer carriage as illustrated in fig2 a for example to enable pivotment of the trailer carriage as it is directed forwardly over the guide rails 14 and 15 overlying.