\Maybe lbl can even be included in the groff suite,
The NOTICE file says:
| Permission is hereby given for its free reproduction and
modification
| for non-commercial purposes, provided that this notice and all
embedded
| copyright notices be retained. Commercial organisations may give
away
| copies as part of their systems provided that they do so without
charge,
| and that they acknowledge the source of the software.
The "without charge" is not compatible with the GPL.
It might be possible that the author is willing to relicense it,
but his
address seems to be out of date.