I need to do the same job on my '72. It is bad on the shelf with a couple of pinholes down in the seat wells around the tranny tunnel. This is not a job that I'm looking forward to and I'll keep putting it off as long as I can. The only times my car gets out a garage these days is when its on a trailer or its at the track. So the rear window seal doesn't get much of a chance to leak. I also took out all of the sound padding that holds water and keeps the rust growing.
If anyone has a rear section similar to what was donated for Shawn's fix...I'm listening. Of course this is after someone donates or locates one for Jeff.