The Sixpacks shown on the planettrout site are not Sixpacks. They appear to be what are referred to as "self-bodied Carey Specials". The self-bodied Carey can use any natural or dyed pheasant rump feather, and uses the same feather for the hackle and wound up the hook shank to form the body (hence, "self-bodied"). The Sixpack falls into the category of the self-bodied Carey as well, but is specifically tied with yellow-dyed pheasant rump feathers. These iridescent gray-green feathers, when dyed yellow turn a rich olive color while retaining their metallic greenish highlights.
The pattern was developed by Carl Haufler in the late 'fifties and was introduced at Pass Lake at the northern end of Whidbey Island, in Washington State's Puget Sound. On that day the fly proved to be so spectacularly successful and Carl was so overwhelmed by fellow anglers offering to buy, beg, borrow or steal an example of the fly that he came up with the simple barter offer which gave the fly its name.
I like a shaggy, unkempt-looking body and usually add a wire rib to reinforce it.