I would compare specific part numbers.
Both the HB racks on my MkI and MkIII look VERY similar, but I literally don't remember if they are identical.
And again, it could vary with manufacturer because the fender/strut assemblies vary between certain MkIII models.
Actually IIRC don't the shock mounts vary slightly between the I, II, and III models? I think some racks like the HB use the shock mounts so just there suggests a difference.