Thanks I got it

 

My guess is that your truck had a door swap at some point. One way to be sure would be to find the frame vin. A real f350 flatbed would hav either a 137" or 161" wheelbase. A super camper special would be 140" and a standard f100 longbed would be 133". Measure the wheelbase and you will at least know what chassis they started with. I'm not sure how a vin # could just get changed like that, maybe the truck came from another state and when it was inspected they issued an f100 title based on the vin. In California the state would probably impound this truck until you could prove that it was not stolen.

 

I am also thinking a door swap is the explanation for the wrong warranty plate from a f100. I cleaned some on the passenger side frame rail but didn't see the frame stamp. It's probably just hiding. I am just concerned about registering the truck in my name.

Old registration has the f100 vin, as do all old insurance documents. Of course I would put an antique tag on it anyway as soon as possible but want to avoid trouble. I will continue to wait to see what a few more have to say

 

My personal feelings are anytime you can screw the government before they screw you go for it.
But if it has been registered as a f100 all this time no one will ever know it unless you point it out to them.