I have seen this done before and it is not an easy conversion. Trying to use 67/8 parts requires extensive sheetmetal modification to the tailpanel and center trunk floor areas they are different between the 67/8 & 69 models. You could mount a flip top lid from a Challenger or Charger to the tailpanel and then fabricate a fuel filler neck/hose to connect to the gas tank, but still there is going to be some fabrication and sheetmetal work involved...................RatPack........