Having driven the section of US 67 north (northeast) of Walnut Ridge, it looks like they could get by using a little bit of the existing roadway once you get past the Current River which sits just east of Pocahontas. The terrain is relatively flat and stays that way until you reach US 160 in MIssouri. Obviously some of the ROW is too close to the existing roadway for it to be used. Case in point, the state line stores right at the MO/AR border. But once you go north of there, it nothing but farmland on both sides of the highway. Then you approach Neelyville where if you blink your eyes 2 times, you're through it. Also the existing 2 lane in the rural areas outside of Neelyville are signed at 60 mph. And of course, the limit drops to 55 once you reach AR.
The "5 lane" section between Walnut Ridge and Pocahontas can't be used since most of the land on both sides is just as high or even higher than the existing roadway. I bet it will either be signed as either 67B or 367.