Don’t listen to that guy, he literally doesn’t know **** about ****. He is just another pathetic forum flipper who begs people for cheaper parts then asks for top dollar for his “newly acquired” parts.
Never trust a printed out picture of a picture of the part you need. Reminds me of the early days of eBay where someone sold a picture of a car for a bunch of money and were bummed out when it showed up in a box.
This difference is going to be the depth of the pulley. Cast pump with have a shallower pulley, where the aluminum will be deeper. I have a 3 groove pulley for a cast driverside pump. Pm me if interested