I fished a 7' 9" 5 weight all the way up to Huggins and never found the casting conditions to be what I would call "tight". My partner was fishing an 8' 6" 5 weight. #71 is a very nice looking campsite with quiet a bit of space, but just because it requires a reservation doesn't mean that everyone who is there will have made those necessary reservations. I have met a lot of people who have not filled out the paperwork for their backcountry permit. There were 2 guys at #70 when we arrived and they weren't sure where or when they were going from there. I don't think I would want to take a large group up to #70 there simply weren't that many good tent sites. You should be fine at #71.
Since I typed my previous post, I have looked at the map a half a dozen times and it looks like the trail stays on the creek from #71 to #70, but I remember it going away. So maybe there is an old trail that follows up the creek. Not sure, maybe someone with more familiarity with the area can answer that. When we were there in May we persisted with dries and just couldn't get a lot of fish to rise. I remember coming back and everyone was saying the same thing "bugs everywhere, no fish rising". One week later everybody was catching them on dries. In March, I would probably plan on a dry with a nymph dropped off of it to see which one they want and then go from there.