The ZF39 is the German designation for a normal scope. This means the ZF39 is mounted on the receiver and has the eye relief as any normal scope has.
Different to this the ZF41 is mounted to the rear sight base. It has an enlarged eye relief. Even if one is to make a mount that allows to put a ZF39 scope on the ZF41 rail, then it would not work, because the eye relief is too large.
(For what it's worth, the Germans also developed the ZF42(B), which never went into production and of which only a handful are known. This is also a large eye relief scope).