I believe that I understand your question and it is "what goes between the top of the windshield and the top cap to lift the top cap up so that the top cap is raised enough to allow the convertible top to fit in under the front of the top cap, Right??
First you are correct that there is a material that must be sandwiched in there to lift the top cap and allow the convertible top to fit in under the front edge. I found some material that was about 1/8 inch thick and 1 and 1/2 inches wide and made for use on convertible tops as a tacking strip. I found this at an auto trim and upholstery shop. It took a bit to determine the best thickness and best placement( forward or back) on top of the windshield to get the right amount of lift. I faintly recall that on the right and left sides I tapered the material or just stopped it a few inches before I got to the right or left hand edge. I also put in a bunch of weather sealer to make sure that any water that came under that cap did not continue on into the car. I might add that I believe that I had to drill out the rivets at least two or three times to complete this so it worked correctly. One more thing is to make sure that you get long enough pop rivets to do the job if you have to use much thickness to lift the top cap. At least one of my pop rivet removals was because I had too short of pop rivets to do the job.
Hope this helps and you are correct there does not seem to be any acknowledgement of the existence of this piece of the car. But you sure can not get the convertible top on the TR4 without having that top cap lifted up off of the windshield.
Charley Fitch
Maintenance Issues
