not sure where you are looking, but I've looked at trucks on the lot and ford build and price and the size is 275/60/20
I've copied/pasted from Build and Price at Ford.ca
SuperCrew® - 4X4
275/60 R20 OWL All-Terrain Tires (A/T) (4x4)
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SuperCrew® - 4X2
275/60 R20 BSW All-Season Tires...
I think the stick tire size on 20’s is 275/60/20 which is 33 inch diameter. Wouldn’t go smaller than that especially with level and any bigger than 295/60/20 which is almost 34 inches. Lots of pictures on here to show you what your options are.
All of the hardware is compatible with aluminum body. Pretty sure it says as much in description. I have them in my alumabody. There’s no drilling and all existing mounting points are used.
Have them on my truck. I’m happy with them. The road noise isn’t noticeable and have done well in the snow. Only 3,000 miles on them but no regrets.