A close examination of a Bessa-R2 and the Zeiss Ikon would lead me to believe that they share the same sub-chassis. There also is some sharing of other parts: exposure-lock button (their actual operation differs), some caps and some knobs and probably the lens mount.
The Zeiss Ikon's body is indeed very rigid.
I haven't handled a Bessa lately, but the use of more metal should give those models more stiffness. There was flex in earlier bodies especially with the plastic back.