1965 mustang k code GT
For everyone who helped me and anyone digging old discussions looking for the answer to my question. I have found and expert that had enough k car examples around my assembly date and knowledge of these cars I feel confident we have a pretty solid answer. The car assembly date has no effect on the answer to this question. The change level follows the engine build date not the car assembly date. The earliest cast iron pump this person had ever seen on an A or Z code car was May 4th 1965. So it is safe to say may 1st 1965 was the day most likely change level 8 kicked in and the cast iron pump was installed. Now like an earlier comment said they had seen multiple cars with may assembly dates in the engine tag with both pumps used either pump would be correct on a car with May engine assembly and very much possible you could have a May assembled engine with an aluminum pump installed (from the factory) as I am sure they had to use up their stock. So the answer is: if you have NO engine tag to go off of and you need to know what pump to use on your car if your engine assembly date was prior to May1, 65 it’s Aluminum and After May 1 it would be cast iron.