Also, I was taught in high school that Liberty Street used to be called “Freiheitstrasse” (meaning “Liberty Street”) prior to WWII (I think, maybe WWI), though I never looked it up myself…

I believe you’re right, by the way, that the allophonic variation after front and back vowels (ichlaut, [ç] vs. achlaut, [x]) has been neutralized to [x] in several Southern dialects, including Alemannisch. German dialectology, particularly along the Rhine, is crazy complicated, but I don’t believe there’s any variety in which the final [x] ever disappears, though. So the Swabian hypothesis doesn’t really stand up–Swabian has weird vowels and some non-standard vocabulary, but it does have that final [x].

I’m curious to know why we called Wurster the “Indian Trails,” and whether that name had been in use in previous generations or if it’s just something we made up.

I take Jim Rees’s description just to mean that at least some final consonant got pronounced, whether [k] or [ch]. In German, the latter is not the same as the beginning of English “chin” but rather resembles what you’d get by very mildly hockering [as in "hockering up a loogie"]. It’s known as an ach-Laut [ach-sound] for Germanic linguists. It’s similar to the ich-Laut — ich-Laut is palatal compared to the velar ach-Laut.

Regarding the absence of expected final [ch] in the local pronunciation of “Bach,” my recollection from my now ancient schooling in the history of German language is that one hallmark of Allemanisch, which includes Schwabisch, is the lack of the usual allophonic alternation between ich-Laut and ach-Laut, which is a pattern typical of standard German. In standard German you always get ich-Laut after front vowels and ach-Laut after back vowels — it’s a parade example of assimilation that can be analyzed by some sort of phonological rule instead of needing to assume that speakers really have two separate sounds in their inventory of possible noises with which to communicate.

But in Allemanisch it’s ach-Laut everywhere, even after front vowels. So even for Schwabisch, I’d expect the ach-Laut still to be there. But the disappearance of that sound from the end — either historically within Allemanisch, or as heard by English-speaking Ann Arborites — is reasonable to expect: The ach-Laut is different from the preceding vowel only in the amount of friction used to make the sound. So there’s a plausible story to tell about why some speakers were going around saying [bach] and other people were hearing just [ba].

It’s very likely the same phonological process that, if he’d lived even longer, would have given us Bo Sembeler from Boch Schembechler.

Yes, well, that was a very long walk around the blo.

but this one says it’s “koak”: [link]

Which is not too helpful, sorry.