I‘ve had a lot of old fords but most were 1/4 or half tons. This one has a ‘79 body on it and the previous owner wasn‘t sure if it was a 3/4 or 1 ton chassis It has 8 lug rims. I‘m wondering if its a dana 60?
It should have a Dana 60 axle, I assume it has full floating axles. Just look under the back of the truck, if it has a coffin shaped inspection cover with a fill plug towards the right side of the cover it is a Dana. The only other possibility is if someone did an axle swap on it.
there should be a tag on the rear axle held on by one of the cover bolts. it will tell what axle gear ratio and diff type.