I did my vent windows on my '66 a couple of months ago. I'm not certain if they are the same as yours but here is what I did. I left my rubber weatherstrip sit out in the Florida sun for a couple of hours to get flexible. Then, I used a little Dawn dish soap to lubricate the rubber so that I could work it into the groove. I still had a difficult time getting the weatherstrip into the groove until I thought of a tool that would help - a screen window tool - the one with the roller on the end that you use to roll the spline into the groove when you are repairing window screens. Worked like a charm. I had trouble with the rivets but I finally did get them to work. Hope this helps. BTW - this is a three beer job!
