For instance, the inversion of verb-adverb ordering in some writing, which seems to originate from Yiddish (e.g., "I now will ask this question" vs "I will now ask this question").
The ordering of adverbs from Old English to the present day has always been somewhat fluid.
"Now, I will ask this question"
"I now will ask this question"
"I will now ask this question"
"I will ask, now, this question"
are all acceptable in both Old English and Modern English. The basic guidance is that the adverb should be "near" the verb, although this guidance is rather loose.
I suspect that all germanic languages have this feature and it would be exceptionally difficult to prise out the Yiddish influence from the general English influence.
Google Ngrams does not seem to support your hypothesis: Using the search terms I now will,I will now,now I will we see that I now will has never been popular, probably as it is a more formal structure.
The same search from 1990 to 2019 shows an equal rise in both I will now and Now I will, but the "I now will" flatlines.
Are there other, comparable instances of a foreign language's grammatical structures/syntax entering into the English lexicon within a similar timeframe?
I cannot agree that there has been a significant influence on English by Yiddish in the way you describe, and what do you mean by "similar timeframe"?
Or are you considering the high Jewish immigration rate of the late 19th/early 20th century and the USA?