Thanks for your help guys.
Yes the backbone has been cut & shortened in an attempt to update it to the later model. This is why the rear end looks odd as it has been rotated forwards & upwards.
My best guess is that the patch on the backbone was the piece that they cut out of the backbone, having those measurements for those bolt holes will help confirm how much I need to rotate the rear end backwards.
The tubes that run down to the swingarm have been cut & bent forward, as those bolt holes currently measure 242 on this frame.
It shouldn't be too hard to put back, I just need an idea of how the shock mounts should look now, the owner could only find B50 shock mount photo's, while they may be similar it will be good to have it looking right.