It sounds like your after Kings from the time frame you're going after.
I used to guide the Alagnak for Katmai Lodge. I can recommend the Alagnak from either Nonvianuk (non-vee-on-uk) Lake or Kukaklek (koo-kok-lek) Lake. It can be about a 5 day adventure from the lakes down to any one of 3 lodges for take-out.
The first portion, from either lake, down to confluence of the two rivers, Alagnak River and Nonvianuk River is a fairly quick ride with some mild white water. From that point on you enter the area of the Alagnak known as "The Braids". This area is home to some of the best trophy sized rainbow fishing in North America with some fish hitting 14 lbs, and plentiful. Also in abundance is Grayling and Arctic Char. After about 14 miles of river you'll start to come to another faster stretch of water and at this point you'll start to find Kings piling up at the ends of the islands because the water forms deep holes. All the rest of the way down you'll be in King and Rainbow water and may still find some abundance of Sockeye and Jacks too given your timeframe. Once you come out of the braids and all the little riverletes combine you'll start to find some slower water with deep holes just right for Kings in the 45 to 60 lb class.
The average water speed is 5-6 knots from the top to the bottom. Great fishing water all the way.
The first lodge you come to is Katmai Lodge, the second Branch Lodge and the Third is Alagnak Lodge. You'ld better get out somewhere at one of these lodges and connect with your charter. Katmai may have a flight that could take you back to King Salmon.
Carry a short barrel Shotgun with you at all times loaded with 3" mag, sequence - 00, 00, slug... Camp a couple hundred feet away from any food you have and you might make it back home
Here are some links that'll help:
Topo Map of the Alagnek centered on the confluence of the Alagnak and the Nonvianuk Branch River Air Service - charter company - float plane fly-ins