The Mo has good numbers of nice size fish. Being a tailwater it is somewhat protected from spring tunoff but can still have rather high flows. If other area streams are blown out, all the guides head to the Mo, so probably avoid weekends.
BWOs. various mayflies, caddis, sow bugs, worms and streamers. Nymphing can be fantastic but look for noses.
If the river is up, a boat would be a bonus. Will you have a boat?