I called the MO Dept of Natural Resources about this, and they really didn't have much information. She said it
should be well marked. No idea how long it will be closed.
Generally when they do this sort of thing, the detour runs from one trailhead to another, which in this case would be from the Claysville trailhead to the North Jefferson trailhead - but she was not certain that the detour ran between these two points.
To get a better idea of the situation, take a look at
this interactive map of the trail. Double-click to zoom in on that area - you'll see that 63 actually crosses the trail between Claysville and JC. Click Hybrid at the top of the map to see a photo view. If you zoom in REAL close, you'll see that 63 is a divided hiway and appears to have shoulders. But that traffic is probably going 65+ MPH. It also looks like no trail access where 63 crosses over the trail.
Hopefully somebody out there can chime in with more info. If not, your best bet may be to call some of the bike shops in Jeff City, or businesses in Hartsburg, to see if anyone knows anything. I wish I had more info, but it seems we're all in the dark here - even the DNR folks.