Neat concepts being tossed about here. I saw the blue duallie photos (see below) on the C10 Forum and thought of this thread, looks like this guy used Ford stepside fenders.
I always thought making a 60-66 dually bed using 57-67 stepside fenders would look good, but after seeing one in person last year the lines just don't flow, IMO.
Another way to go would be something along the lines of the last photo below. If I had seen the photo before I started the modifications on my '65 I would have taken a stab at it.
The idea of widening a stock stepside is a good one. I widened mine 4 inches, wasn't that tough to do.