just did my 65 Gmc same thing .just drill out old rivets and peal it apart,paint and replace . rubber is a bit of work to slide on but a little vasaline makes it go easy.when you atach vent window rivet get someone to help.hold the fixture while you peen the rivet . also mask any new paint when you peen rivets . I drilled out a piece of 1/4 x 1/4 piece of steel to put in vice to set rivet head in so it does not flatten head . check holes on vent frame and glase frame sometimes gm hade 2 different size holes here then you would need a rivet with a step in it.
Hans
