The 'TD' is the wagon.  I've got a '79 300TD.  This is the W123 body
style and I believe the wagon was manufactured from MY '79 to '83.

If it's got the third-row seat, it folds down flush with the bed.
Indeed, looking at how much space is there I can't imagine the third-row
is comfortable in any way.

The second row seats fold flat.  The bottoms fold up so they touch the
backs of the front seats, and the backs fold down into that space.  I'm
6'2" and can collapse the back seats fine, although the bottoms get
squished a bit.  The bottoms can be removed entirely if so-desireable,
but it only gives you about 6" more room.  There are "release levers" on
the bottoms so removal is tool-free.  FWIW, I keep a 12V air compressor
and a box of Kleenex on the floor behind the driver seat, and I can
still fold the back seat just fine.

So yeah, all told, everything folds flat.  Leaving the seat bottoms in
place, there's maybe 5.5', 66", or 170cm in there front-to-back.  I'm
not super-sure about that, but I do know that I can't lie down back
there.  With the second row of seats up, I think there's maybe three or
three and a half feet (around a meter) between the door and the seat
back, and I think it's about the same width.

-tom!

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