In 1955, Porsche changed the crankcase of their standard pushrod engines from the VW two-piece casting to their own three-piece crankcase. The earlier crankcases were then known as "two piece" and the younger, then current production was identified as "three piece" in the nomenclature.
Along with this change came wider cylinder head stud spacing which could accommodate larger diameter pistons.For practical reasons, the engine remained basically unchanged..
This cylinder is most similar to the earlier 80mm bore example used in the two-piece crankcase 1500. It differs in these ways:
In the image below, you can see the fin shape, nearly identical to the earlier 80mm bore version it copies.
In the image below, there's not a lot of detail extra that can be discerned, but perhaps a bit of perspective on wall thickness - it's second in thickest wall ever provided in an aluminum cylinder, the champion in that regard being the even more rare 75.5mm cylinder of the 1300S (two piece crankcase).