After months of trying to find pinouts for various Digimatic indicators, I stumbled on this link to an actual manual ("Handbuch"). It's in English. It even covers the presetter.
If this is keyword spamming, I apologize. I added enough keywords to help others, like me, find it in the future. I found it by looking for the 543 Digimatic Presetter, which might not be pellucidly obvious to someone just dealing with Mitutoyo SPC output.
Link:
https://www.labviewforum.de/attachment.php?aid=21297