I don't know what ACA has planned for the route between Ash Fork - AZ and Williams - AZ. As far as I know the original Route 66 is completely replaced by Interstate 40. To bypass this 19 mile long section involving 1600 ft of climbing, I took today County Rd 142, also signed as Double A Ranch Rd, out of Ash Fork. After 4.8 mi the road changes to FR-124 but keeps its name Double A Ranch Rd. It soon becomes a dirt road with a good red-brick surface, until it gets paved again a couple of miles before Williams. It is a rolling, very scenic road. Of course it also involves at least 1600 ft of climbing and totals 29 miles, but in a quiet setting without diesel fumes. Dirt roads are also less risky for punctures than the shoulders of Interstates. Part of FR-124 runs along the Santa Fe railway. I saw 8 freight trains passing in the 2 hours I was on this road, more than cars and motorcycles. There is no way of getting lost if you keep the two numbers County Rd 142 and FR-124 in mind, because the main road is much broader and much better maintained than the side roads ending on it. While a dirt road may not be liked by all cyclists, I would recommend it at least for eastbound Route 66 travel. Westbounders might try to outpace the heavy trucks descending on the Interstate.