[Bruce Edwards]

Dave,

You should ALWAYS put the windshield together before you try to cut any holes in the body. Use the marks on the body as a guide for the cuts only. We place heavy tape on the car to help mark the area for the slots. If the supports for the windsield are on the outside of the supports on the frame of the car use spacers do not try to pull over to fit you WILL break the glass.
I do think it is a good idea to use the center support. However most of the cars you see do not have this due to the windshield being layed back to "Race" angle. Check you side curtains if you have them to be sure of the windshield angle.
The windshield frame seal will keep the frame off the finish but it is my opinion that the frame be on the car for added support not held up off the body. The windshield frames are not strong at all and can use all the help they can get. More so if you are going to run your car with a top.