Sorry but my info was abbreviated/incomplete for easy of post. Also your output if 1.78 (16x9) should be 640x360 (you must keep Anamorphic as Strict when using a DVD)*. A DVD is 720x480 which is 1.5 and not 1.78 (16x9). A DVD uses non square pixels and a 1.78 picture is vertically squeezed to 1.5 to fit on a DVD. It is then un-squizzed back to 1.78 before it's sent out. This is the anamorphic process in a DVD. You can't have a 720x480 because it's the wrong aspect ratio. This is way the resplution must be changed to 640x360=1.78 or 16x9.
*I've never done a DVD in HB, only BD's.