Abstract: An apparatus for stacking, registering and attaching one or multiple sets of electrophotographic printing machine output. The copy sheets are discharged from the machine and fall into an inclined compiling tray and are longitudinally registered by flexible, endless belts contacting the top surface of each sheet. Each sheet is then laterally shifted by a tamping mechanism which has upwardly flared baffle to corrugate the sheet as it is shifted to increase the sheet beam strength and facilitate easier and more complete registration. The discharge nip assembly which includes the flexible belts is vertically adjustable either based on discharged sheet count or in response to feedback from a stack height sensor so as to maintain optimum contact by the endless registration belt and allow for high capacity compiling. The compiling tray can also be adjustable.