Rear bench seat (SWB) with a plywood base?

Please could someone enlighten me from which series model the rear bench seat comes from which have a Plywood base and is not just the cushion siting on on the frame.
I need to fit one to match the only one fitted. My land rover series 2 is not standard and has no seat frame, but is fitted with a metal frame and wood panel.
They come up very occasionally on fleebay so I assume were fitted as standard on some models, I just don't know which ones. The measurements are the same as the 2, 2a &3. I am begging to think they might have been on a series 1 but just cant find out.
Any helpful knowledge appreciated so I can avoid making them.

Pictures always help With something like this to give so people can see exactly what you are talking about.

My 1977 series 3 station wagon has a rear bench seat with a wooden base and back panal. It is on a hinged frame so that the seat can be pushed up against the front seats and the back folded down. Its bloody heavy and awkward to manouvre.

Col

I bought this off EBay
It’s light and neat but a bit buggered at the moment, two lugs on back panel slide into the slots on the galvanised capping rail, I used 2 nutserts to retain the base it come out no bother if you need to the cushion cover has gone but that had a lace on to tie it in up position. Got some new material to suit the elephant hide on the to do list
not seen ply rear seat bases but the fronts have them

Sorry trying to upload some pics but it appears I don't have permission.

Stumbling with the Tec today. So the seat appears standard Land Rover and not bespoke. I am trying to match it for the other side, there are no back panels. It know the front ones come with a base bur it seems some of the rear do as well.
Thanks for the input folks.