Sorry for the tardy replies. My device allows me to read MN, but not post while away from the shop. Kinda on purpose...
Not whalebone. I have maintained it for the past 25 or so years. It's provenance begins with the Hill's in the early 20th c. It has a beautiful Hill Certificate from the early 20th c. It came to the US through the Waddell Collection. The Hill cert says Stainer 1650's. The back gets referred to, lovingly, as a 3 pc back, wings upper and lower. It ended up on this coast via. Armin Schlieps.
It does need some work, but the owner is elderly and these things should perhaps be done between owners.