I have a porter platius and and I had inherit from one of our rallies at muncie after it had gone in , I rebuilt it and got it flying if you build a drop box for it mount the drop box so that your jumper is centered on the CG of aircraft. I now have 25 flights on mine since then and with a 90magnumXL with a 13/7 prop on it boy does it haul the mail . with about 10 pecent flaps it will get you to a good drop altitude in about 2 to 3 min.
BOB
fair winds and blue skies