The original two-part board with a square of black vinyl covering the hole for the wire-wheel clamp ... (image from Clausager)
... and the simple hinges used for both that and the seat back (drawing from Leyland Parts Catalogue)
From October 73 a one-piece board was used (with the same square of black vinyl covering the hole) ...
... with a more complex hinge that pivoted both the board and the seat-back. Press stud for carpet arrowed.
The seatback is processed wood with threaded inserts for the hinge screws.
The two end sections of the hinge (arrowed) attach both the board (raised) and the seat-back to the body.
A general view of the load-space board in the raised position, the V8 wheel is stored upside down which give useful additional storage space ...
... and the very simple hook to hold the board up ...
Uncovered 'luggage' (cover fitted but folded forwards over the rear seat back out of the way)
Covered and pretty-well invisible, especially with the hatch shut through tinted glass.
Cover made long enough for when the rear seat back is folded forwards for more luggage, tucked up underneath itself when not in use.