THIS IS ON BUCKETS SETUP:

70/71 foams and 72/74 are diff foams
of course, covers too to fit on foams ( same years )

SEAT BACK changed on mid 71 production line, from a large release button and metallic hinge covers to a one piece seat back panels, covering hinges and smaller release back button. This of course makes a diff back frame, back panel, back release system. So you'll need to take care about that when finding replacements if needed.

tracks are the same.

now, DUNNO if benchs got somekind of differences like these