I also have an 03 aviator. Me and 03Aviator both used one of these I believe:
http://www.installer-data.com/item/disp ... it=95-5026
If you have the same mounting like an aviator, it might work. It's weird that crutchfield didn't carry the double din for an aviator, that's where I got mine. I called them though and asked them about it. Maybe if you called them.
They do make a single din:
http://www.installer-data.com/item/disp ... it=99-5026
But that's usually for people who don't quite have a hole the size of a double din.
I don't know what your 350 dash looks like, but installer.com has this for 05-06:
http://www.installer-data.com/item/disp ... it=95-5812
I didn't see the any for 03's. But there might not be enough room (at least as they say). Also other forums might have more F350 info. I don't know any personally, but I'm sure there are some out there.