I think the "Rubberlegs", a Western favorite, would make a killer Stonefly for Czech nymphing- it quick to tie, it has a mottled appearance, can acccomodate whatever amount of weight you want, and has nice wiggly appendages.
Be aware that one thing Aaron & I have learned is that you don't need as much weight in your anchor fly as you might think, except in really fast, deep water. At one point we were using #8 2-3x long hooks with 5/32 tungsten beads and 15-20 wraps of .030 lead wire, now we have lightened way up. I'm currently using a 1/8 tungsten bead and .020 lead on 2/3 the shank of a #10 scud hook for my heavy fly now, and sometimes it's too heavy. As the hatches get cranking and fish move into shallow riffles, 2 smaller, modestly weighted flies should be more than enough- I seem to keep going lighter as the season progresses. You don't need to dredge the bottom, but merely to be near it and fishing slower than the surface current.