I've removed and replaced several Vintage Speedster Windshields over the years and always had problems getting the rubber base seal to lay flush against the dash like it was before I removed it. Well, this weekend I learned the secret.
Kirk allowed me to watch while his window installation expert installed a windshield. It turns out that even though one person can do it, it's really a three man job.
The window is fully assembled to start with. Window is placed in base gasket, upper frame is placed on windshield and posts are attached. Then, the assembled window is placed on the car and while one person tightens the center post, two others, on each side of the car, are pressing on the top of the windshield and down and toward the back of the car with one hand and pressing in on the post with the other hand. They keep the pressure on while the 3rd person tightens the posts. This causes the windshield to tilt to the rear so the base sits flush against the dash.
It was interesting to see how much flexing the windshield can actually take. What the windshield won't tolerate is being touched by any of the four screws that hold the post to the frame.
Now you know the secret and thanks to Kirk for letting me watch.