Not having the best of luck with this at all. I contacted RA on Wed via phone, then last night sent detailed pictures showing the visual difference and here is the response I received this morning.
"Dear Chris Nelson, Thank you for your email. From your photos, it appears you received the pump you ordered, The part number on the manufacturer's box is correct and the pump body matches the image of the WPN079 we offer in our catalog. Looking at the pump, there isn't sufficient room to install a larger impeller, as it would bind against the inside of the pump body. If the pump won't work for you, you may return it for a refund."
I am going to call one last time and mention a few members who also received the wrong pump. I will then take a chance with swapping this one for another with fingers crossed. I was told they would not measure the pump similar to what they told you Gareth J.