In 1955, the Glass-Fibre top was available for that year, but NOT with a port hole. One of the main complaints about the '55 was that top blocking your view around that top. So in 1956, they added the port hole to that years top. It was a Standard feature for 1956-1957, but you could still get a top without the port hole. However, 90% of the tops supplied in '56 had the port holes in them. Here is what Automotive Mile Posts has to say about this.