I'm not sure they came with 9' or 8' beds.
The F-350 did have a different wheel base than a long bed F-150 or 250. I believe it was to accommodate the chassis cab set up like on GM dually C/K30's. Here's a couple of pictures of F-350's.
You'll notice the passenger side spare tire carrier. I have only ever seen this on the F-350. This allowed a second fuel tank behind the rear axle. Due to the compartment and size of the spare, the rear axle is set back further (about 8"; 140" WB). You can also see in photo #1 it has 33x12.50x16.5 tires on the rear. I believe they were optional. If you ran the same size tire front and back like in photo #2 & 3, the rears would track inboard of the front.
If you want more info on the truck you can get a Marti Report.
Here's the specs on the 460: 212 HP @ 4,400 rpm & 342 TQ @ 2,600 rpm.
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