That's odd, bc. I checked the link to be sure it's correct and it is. In the search box at the very top of the page enter 'Contributions to the Montana Historical Society. It's unforgiving, you must enter it exactly. Set at 'all media types' (the default) and hit 'go'. All volumes will come up. You'll find they are available in multiple formats; read online, kindle, pdf, etc.
The pictures above are from Volume 4 which has a 'grand and gallant' article (I think it's fun to read these old stories!) on the LBH and Knipe's 1903 account. I came across it from Gordie's notes. He referenced the pictures as being taken before the road was constructed and the markers moved.
Most of Bradley's papers were reprinted in these volumes as well. They're in Volumes 2, 3, 8 and 9 and included are his writings on such subjects the early (1830's) history of Ft Benton, histories of the Sioux and Crow, the great smallpox epidemics, early visits west by Audubon and all kinds of other fascinating stuff.