I pulled out my 65 Fold-down seat and see it still has the part number on the back side of the seat (the flat seat part).
The mesh is 0.5x0.5 center to center of the wire mesh. It's approx 0.040 thick.
The padding is actually foam. This matches what's on my 67 as well. My 70 does not have a fold-down.
The seat bottom has the burlap with wire.
(added the term fold-down on my last two
posts for clarity)