I've run those trails plenty of times. Some are a little more dangerous (ankle twisting) - but some are fine. If you park at Newmans, cross the street, head straight in, with the river on your right, and just keep following that trail, it's pretty good for running. If you continue to the first street crossing, it's 2 miles (there and back), you can continue past that street and keep going.
If you park at Newmans and cross the wooden pedestrian bridge, make the right, cross the river, make a right sothe reservoir is on your right, keep going all the way to the fence at Chimney Rock Road, hop on Chimney Rock Road and cross the bridge, into the next gate, and follow that back, that is also a 2 mile loop. Hope this makes sense as directions are not my strong point