I made my comment before all this other info was given. I could certainly see it was not an 8-lug Napco and I thought the truck looked like it had the bigger sheet metal up front. I've owned a Napco, even rebuilt the front axle, so I know what the Napco axles look like.
This picture has been on the internet as long as I have. I've always wondered what it's story is. Appears to be a similar conversion
I see the bigger ones with the wide 6-lug pattern and 10-lug. I've seen medium duty Fords Napcos with the wide 5. I guess it depends on what rating rear they have