Ray, I really can't tell you what they're worth, as that's very subjective and dependant on so many factors.
I just wanted to tell you that Ron A. had one years ago stored over at Mark's Fun Farm, out back. This was in the late '80's when I was at Mark's working on our Special Coupe. The blindback was very complete, and it included that curved aluminum tack strip that goes from one side to the other in one piece. I knew then that there weren't a lot of those '29 blindbacks, and, that it had to be pretty difficult to find that tack strip. I'm not sure where that sedan went. Maybe it's the one you're looking at now. Wouldn't that be a "small world" item?
Give us a lot of photos and details, and I'll bet you'll get a lot of opinions on the value.
Dave Lopes