I recently saw a reference to a Holga mod, turning the holga panoramic into a lovely 6x12 camera with a Schneider Kreuznach lens. Unfortunately, the HolgaGon instructions seem to be no longer available via the link that was mentioned. Does someone here happen to have a copy of the PDF?
I don't have a copy of the pdf you want, but here is part one of several blog posts dedicated to making a HolgaGon. It might help. There is a link to a pdf, maybe the one you are looking for, but the link is appears to be dead. Good luck!