I would try two more things.
Use the fsck with the full option on the volume name not on the disk.
fsck -F <fstype> -o full < raw volume/slice name>
Also, you might try adding a new superblock. You should have a file that lists Alt superblocks. On my HPUX system it is under /var/adm/sbtab. Try 16, I believe there is an extra one there.
fsck -F <fstype> -b 16 <raw volume/slice name>
Failing all that, you may have to restore the disk.
Hope this helps!!