I have a 2004 libra are the rear wishbone identical as I have the rear end of one that is different to the other but the alignment and ride height are the same.

Not necessarily! The original type mounted to the tub via ball joints were (allegedly) superceded by one mounted via cushion joints, which theoretically gave advantages. To confuse further, there were two ways of connecting the early type ball join to with the tub. Initially, four separate brackets were used each side; later, this arrangement was altered so that only two, but longer brackets were employed.

In every case, the dimensions of the arms themselves is the same, and I suppose they could be mixed, as seems to be the case with your car. Without seeing pics of the two sorts you have, it's hard to say much more. Maybe your car has had a "diversion" at some time, necessitating replacement with whatever was then available.

Thanks Cabrera I will try and take some decent photographs to post.