Stu is correct
In regards to the hook. to get the true intent of the pattern it needs to be tied on a large heavy wire hook 2/0 for shallow tail outs annd up to 5/0 for other locations depending on depth and speed. The commercialy available ones tied on 2's totally defeat the purpose.. This fly is designed to be fished on the swing with a floating line. The hook needs to be large and heavy.. Also the olive Bill used was not really olive but a drab yellowish green not a dark olive. I know he always had a difficult time finding the proper Olive calftail to suit his need for that fly and the Washougal Olive
Only steelhead matter!