Ray, this is the pattern I developed quite a few years ago to fish the Stones here on my home waters. It is tyed on a Mustad 79580 Streamer hook. I gave up on the curved hooks awhile ago. I am not convinced they come loose from a fish's mouth faster than a straight shank, but I guess it's a confidence thing for me. I tie them mostly on a size 10 to size 6, but go all the way up to a size 2. Size 10 to 6 is a bit smaller than the Giant Stone nymphs, but I feel it covers the other Stone nymphs (Golden, Little Black, and Skwala) that are present in my rivers quite nicely. I start using them around St. Pattys Day. Seems like the Nymphs are stirring around more as the water warms a bit. I use them till, well now, when the runoff starts to subside and the other hatch's are starting. Caddis, Baetis, etc.
Rarely do I have high number fish days on these patterns, but on the Freestone Rivers, this pattern usually accounts for the largest fish of the season for me.
Hook - Mustad 79580 sizes 10 - 2
Thread - Olive Dun, but use what you like. I do
Dubbing Ball - Kaufmans Brown Stone Dubbing
Tail - Gold Goose Biots Forked (Brown and Black are more popular)
Thorax - On each side of the hook lay 30lb Mono (gonna try some 60lb) along side. Tie it in, and it makes a nifty flat thorax. Use Lead wire if you like. Wrap D rib over to make the thorax. The pic has Olive/Brown, but I also use Black, Brown, Amber, and even Red.
Abdomen- Kaufmans Brown Stone Dubbing
Wingcase - Pheasant, Turkey, or Thinskin. I prefer Pheasant
Underwing (legs)- Brown Partridge