Need fuel pump help

I need to order a new fuel pump for my 41' Pontiac. How do I tell if it is a single diaphram or a double diaphram. Its for the stock I-6.

 

I believe that a double diaphram pump would be one that has additional parts to make vacuum wipers work off the fuel pump. It kind of looks like two fuel pumps stuck together. If you have both vacuum AND fuel lines hooked to the pump it would be dual diaphram.