Bruce,
I remember reading that the Northrop flying wing suffered stability problems when they removed the props and put on/in jets. I also remember that the reason was the fairings over the driveshats acting as fins. These fairings were removed when the driveshafts were removed, then they found they needed fins on the jets. The props don't provide the stabilizing influence and the B-35 had counterrotating props so any stabilizing effect of nonaligned flow going thru the prop blades would have been cancelled out anyway.