If you have an E39A vr4 you can fit the complete GTO rear trailing arms and use the drum type handbrake setup.
I'd be interested to know the bolt spacing on the GTO caliper mounts and the offset of the mounts from the disc centre line, s I've been lent an FD3S front brake setup and the calipers look very similar (also made by sumitomo).
The FD3S calipers have a 158mm bolt spacing (centre to centre) and 35mm from the disc centre line to the closer surface of the caliper mounts.