I've been able to fish many of the famous hatchs' in various regions of the country and there are a few patterns that seem to work everywhere I ever cast them. Adams, Light Cahill, Grey Fox, (you just change dubbing to make the fox into brown drakes and etc. very versatile pattern) Little Blue Quill, are a couple I don't go without if dry fly fishing. The Blue Quill is always #18 or 20, and fished no matter what's on the water. Most places with healthy May Fly populations have the Batis (blue wing olive) the Blue Quill will do for almost all of them.
For caddis; if they have slate or brown wings I like the Heneryville Caddis. It's another that you just change body color and have the game covered. Brook Trout = Elk Hair Caddis & Bi Visible and you're good to go there.
For Montana in late june early July, don't forget your 'Sofa Pillow' (salmon fly patterns)
You may like this thread; A Thread for the Dry Fly Purist;
a couple people posted some flies, unfortunately one of them must have deleted them from the host because they are no longer there. I put a few on page #7 and there may be more I forgot about.
One of these days I'll make a new dry fly thread and load it up with the old school patterns.......