I have been wanting to do this river for several years, and finally did it at a flow of 350-400cfs. First, the hiking involved is harder than the river, which now I know has had belated ratings attached to it, IMO. The first canyon is almost all class II, with one or two rapids that may be class III, depends on who you ask. The second canyon did have some class III, but was not as hard as the class III on guardrail on Willow Creek, but they are interesting in sections, when the river narrows down.
We took out at Colorado, a road by a communication thingy, about mile 187 Parks Highway or so. Park car at the gate on the right fork of the road, which is about a mile down the road. The put in is on the trail right across the tracks as you cross Middle Fork Chuilitna. The trail fades as you make your way around swamps with standing water, you will see a bluff in the distance, a few miles in, walk to it and summit. From here, head right back to the swamps to the headwater of the first canyon which you can see, or just bush wack straight down through fairly heavy brush, 20 minutes to the river from the knob. The entire hike in is probably about 5 miles.
After the second canyon ends, a small stream comes in on river right, your trail out is across from that. The hike out is about 5-6 miles, but is on a road. The hike in starts on the trail, but there is alot of swamp to cross and bushwacking too. I'm not going back, but I had to do it once I guess.