I haven't fished the MO, or Montana for that matter. Most of my trout swinging was smaller streams in the east, the streams in eastern Yellowstone, and some in OR.
That said, my single most productive fly has been a small sculpin (2 in-ish), usually fished on a sinking poly leader. Second would be soft hackels, fished in tandem. I don't fish blind so much as fish structure/holding lies, and more often than not use a Leisenring Lift approach, trying to set the fly up for the swing from the original cast placement, estimate of the drift/sink path- which may or may not involve some mending- and then to present the fly swinging through my target zone, with tension, possibly some lifting, and probably about half the time with imparted action.Action can be in the form of tip twitches, arm pumps, a wiggling of the rod hand (most often with soft hackles on the lift).
If I wanted to catch a ton of fish I'd be euro nymphing. It has zero appeal to me. The approach above is so much fun to me I've fished through several excellent hatches, fish rising all around, a dry fly rig on the bank, me happily swinging some fish on the small spey.