Get yourself a 1/4" metal plate that will cover the opening on the transmission - drain the transmission, remove the PTO box and trace the box opening/ hole location using the old gasket on the metal plate - trim/drill the plate and install. You will be much happier with it removed as it's a GREAT head knocker under your truck when you working under there. After it's removed you can add it to your iron pile as it's not GMC specific and worthy of saving - as no body will use it again.
