I'm kinda confused on what your plans are, are you going from the dome all the way down to fontana lake and then all the way back up to the dome or are you just going down to 71 and then back up?
From the dome it's only about 9 miles down to 71 so you could easily do that and have plenty of time to fish in 4 days. Since you are going downhill and if you are in reasonably good shape, i would think you could do that hike in under 4 hours pretty easy, but that's just my guesstimate. If you are going with someone else (i assume you are), you could leave one car at the end of the road to nowhere and another at the top of the dome to save you the trip back up the dome, but i've heard some stories about vandalism and so forth at the end of the road to nowhere. We are trying to avoid leaving a vehicle there at all costs on our planned trip to the area.
Anyways, i hope this helps some. If you could maybe clear up your plans a little more then i would have a better idea of what your intentions are.