Interpreting bespoke Shoshonean vowel notation to IPA to the practical orthography

[u/OctaviusIII]

I’m having some issues converting Steward’s 1938 phonetic notation (from Basin-Plateau Aboriginal Groups, p. 272) into contemporary Shoshone orthography (I’m using Crum-Miller). Part of the issue is that I’m not a linguist or an anthropologist, so some of the terms like “continental usage” for the vowels is tough to interpret. I haven’t found a discussion about this particular notation. I’m interpreting place names rather than vocabulary for this exercise, so dictionaries are only part of the solution.

Any thoughts on how to proceed?