Nice, Tony! Is that foam for the "wing cases"? Chamois? Bugskin?
I found a nice material I like for nymphs, and it makes decent stonefly patterns. The material is called "plastic canvas" yarn. It's a nylon yarn you can get at craft stores, comes in lots of colors, and is cheap. It's translucent so it looks like tissue and chitin. I use an off-white or pale yellow for the ventral side, then pull a length of contrasting color for the dorsal side. I rib the abdomen with wire and then pinch the abdomen to make it dorso-ventrally flattened. Contrasty details are added with a very fine point indelible marker (drafting pen), and with vinyl fabric paint for eyes and on the thoracic plates. The nylon holds the color pretty well, and they can be touched up later.
Tails and legs I use vary, and seem to matter little. When I tied these, rubber legs fine enough weren't available -I believe that's changed and there are some nice variegated materials out there. I've also used feather barbs. Regardless, that may just be human eye candy -tufts of fuzz work just fine -it's the body shape, size and shades that I think matter most. The picked out fuzzy legs also stabilize the fly on the drift and with the flat abdomen it planes on the drift with a nice upright, slightly tail down attitude -although real stoneflies dislodged get to bottom very quickly swimming with a head down attitude with legs a-flailing in a notable wave-like pattern of motion. Impressive swimmers. To mimic this I saw a pattern that used rabbit fur for legs that rippled in that wave pattern. I never worked with that though. That with lead eyes, or a jig head, might make the ultimate dislodged stone. My simpler versions below have worked really well for me though.
Anyway, the body material is pretty cool, and you could go much more realistic if you wanted to get fancy.
Here are some already tied, and fished, from my nymph box.