[Kube]

Andy, You do not have to remove the upholstery to make your cushion have the feel of a nice - new couch. Old upholstery is not too agreeable to removing and reinstalling.
Remove the seat cushion and flip it over on your workbench.
Acquire some carpet padding - the foam rubber stuff.
For a '39 coupe seat, cut 12" lengths of the padding in 7" widths.
Roll up a length (tightly as you are able) and stuff it in each individual spring. Once you "let go" of the padding it will "swell" in place.
You will find it easier when stuffing to twist the padding as you press it in.
You will be AMAZED at how nice the seat is when done.

Oh, you may have to cut the burlap bags that surround each coil.