I agree with Scott that Walter at Parks Fly Shop would be a good choice for fly hatches, and up to date info. closer to the time of your trip.

However, I would not recommend wet wading as a sure bet at that time of year in the Lamar. It may be possible for some, but it could still be quite cold, and still experiencing some run-off until mid-to-late July, depending on this winter's snowpack - and we won't know that until next March or April, or so. If it is too high fo wet wading, there are also places to fish from the bank, if required.

A 9' 5 wt Rod will work just fine.