If I remember correctly, like Wolfgang assumed, there is a bow attached to the top bows, that hugs the rear deck with a bolted tab in the center. The bow is sewn into the top material. The rear of the top sits on the deck when the top is retracted.
On some Thunder Ranch cars, a dress molding (fiberglass) sits on top of the rear deck, held in place with bolts. A piece of heavy but pliable plastic is sewn into the back edge of the top. When the top is put up, the bolts holding the rear molding are loosened, the plastic is tucked under rear molding and the bolts tightened. When the windshield clips are connected and top bows are up and locked, it tightens the top no snaps used.
Hope this helps.