Tires aren't nearly as important as riding within your abilities. Many have traversed those roads in poor conditions on road tires with no issues, while many others have used full knobbies and crashed. The K60s will be fine as long as you don't ride faster than your skills allow. Just remember that the 50MPH speed limit is just that, a maximum posted limit, it's not a requirement of speed to be maintained. If you're more comfortable riding at 30MPH, do so (just keep an eye on your mirrors so you can get out of the way of approaching trucks).