When I replaced the vent rubbers in a 53 Allstate, I started from the bottom and worked my way up. I used a soft plastic bondo spreader with a rounded edge in addition to some dish washing liquid to act as a lubricant. As you insert the rubber, tug on it a bit as it does need a little stretching to fit properly...at least mine did. I assemebled everything outside the car and then installed it in the car. While it's loose in the car, install the door glass.
