Now for a quick update -- the interior is in good shape, but as the vinyl was cracking/splitting at the seams in several spots of the inserts and the foam had become uncomfortable (to me) in parts, I decided to redo the seats completely. I followed
@sixpkrt's suggestion for an upholsterer, and the photos I have received so far indicate this was the right choice -- thanks Tim!
The upholsterer told me that Medina's front bucket inserts had been redone once before, because the material was not quite the same as the material on the sides. At his recommendation, we ended up replacing the entire vinyl (inserts and sides) with original material, as well as inserting new foam where needed -- the springs were OK.
Here is what the seats looked like before:
Here is what the driver's seat looks like now. The pictures are a bit distorted, but that's all I have for the time being:
Note the triple seams in the corners. Here is a close-up picture during the operation, showing the corner seams of one of Medina's buckets. As I said, original material and workmanship except for the seat bottom and seat back inserts.
Here are photos of
@saforwardlook's 1971 Monaco, which has a superb original black buckets interior. Note the same triple seam in the bottom but the single seams in the setback's upper corners.
Here is a photo from
@71Polara383's 1971 Monaco ("Pennsylvania"), which he parted last fall. The interior is also original. Note the triple seams all over, as in Medina!
Bottom line -- there seems to have been variations in the seat production...