Leland is the owner of speakerhardware. Leland is a forum member, authorised builder par excellance and helps a lot of us out with some harder to source bits and pieces.
He won't be fibbing if he says he's busy.
Bill will need to answer, but that would require a redraw of the design as well.
My thought is that modifying the/any part of Bill's design(s), which is based on TS parameters of the recommended drivers, immediately makes cabs a lottery. Crossover points may need redefining, meaning changes in the filters themselves.
Performance then becomes an unknown quantity.
The age old adage here, is follow the plans to get expected results.
Hope this helps...