I’m looking to get an aluminum water pump for my 66 Mustang with a 289. Some of them come with the backing plate and some do not, what’s the deal? I’m pretty sure the cast iron one on there now has a backing plate why would aluminum come with no backing plate? Is it just a different style pump that doesn’t require it to have a backing plate? BTW, these are standard rotation passenger side outlet water pumps Im looking at.