Montana Mid July Recommendations

I am looking for advice on a week long trip to Montana next summer in mid July. We are heading to Glacier for a week at the end of the month, and I am planning to do a week long fishing trip with some friends before heading up to the park. I am worried about the temperature because I have seen lots of angst about hoot owl restrictions and early days.

Ideally we'd like to fish the Missouri, or somewhere we will decent expectations of big fish and cooler water. Any advice on places to hit? Are we good with the Missouri in mid July or should we look elsewhere?