Funny you should bring this up... I just watched The Secret Beyond the Door, which was filmed in the late 1940s and directed by Fritz Lang, and of course starred JB. If the rights thing had been able to be worked out, and, of course, had the ABC technicians had better editing equipment available to them (you would not believe the editing set-up they had in 1967), it would have worked perfectly to have had a couple of snippets from Secret Beyond the Door as part of the 1949 flashbacks.
It's tempting to think of Secret as a lost episode of DS. It has larger-than-life performances by a great ensemble cast (I particularly enjoyed the performances by Natalie Schafer and Anne Revere). Michael Redgrave could be Barnabas with a slightly more raw, psychotic edge. And Joan's voiceovers throughout really do give you that "Collinwood" feeling.
Sadly not available on DVD, but the VHS I got from the library looked gorgeous.
G.