The new spring has been redesigned with coils at the front corners. The original spring only used flat springs.
The linen backing for most of those seats usually looks like Jim's when disassembled. We always have an upholserer sew new linene on with the seams running in between the linear stuffing strips. This is the way leather seats were constructed, but they may have done some "Tex" seats that way.
I have never seen molded foam cushions on those seats although leather did have 3/4 inch thick slabs of foam attached to the outer sides of the synthetic horse hair. The construction and retention system of these seats requires a minimum of stiffness of the cushion to hold the seat together. I have seen hundreds of seats with the bottom cardboard retaining pleat unraveled and loose due to this problem.
Bosch Master, ASE Master, L1
33 years MB technician