'Without so much as a call or a letter – he showed up.' Is this grammatically correct?

Is the sentence below grammatically correct?

Without so much as a call or a letter – he showed up.

I know that dashes can be used to emphasize parenthetical information, but I feel as though the parenthetical element typically comes within a set of dashes or after a single dash, not before. After all, dashes typically draw attention to and emphasize what comes after (or within).

Therefore, does placing a dash after a parenthetical element still draw attention to the parenthetical element, or does it draw attention to the independent clause? Is it even grammatically correct to use a dash in a sentence with a parenthetical element to emphasize the independent clause rather than the parenthetical?

Here’s an example of what I’m wondering:

He showed up – without so much as a call or a letter. (The emphasis on "without so much…" in this sentence, yes?)

Without so much as a call or a letter – he showed up. (The emphasis is on "…he showed up" in this sentence, yes? But is this grammatically appropriate? Stylistically?)

Thank you!