That style truck (Pictured) actually was first out in '66 (Fall of '65 is correct). Although the Doors on '67-'72 Pick-ups look similar to the ones on your 5500, they are different. Not real sure if the Weatherstripping could possible be the same, but you could check on some part numbers or just try one for an experiment. I would also contact GMC parts (Volvo now) and see if any are still available new for your truck. Not real sure when the last cab was made, but believe it went well into the '90's.
Keep us posted on your project.
Bill
