68 is a one year only deal because of the round markers. that being said, I have a later Duster fender that came with a rectangle side marker on my 67 Valiant that came without any marker at all.
The headlight bucket is a little different too but wasn't an insurmountable problem. find a Duster fender through 1972 if you can't find the correct one and fill the hole, re-drill for the round marker and make `er fit!