So in talking to some friends tonight I find myself looking up Zeta Gundam designs. And apparently nobody will cop to designing the Bolinoak Sammahn. And... I get that, and yet I want to know.

https://ja.wikipedia.org/wiki/%E3%83%86%E3%82%A3%E3%82%BF%E3%83%BC%E3%83%B3%E3%82%BA%E3%81%AE%E6%A9%9F%E5%8B%95%E5%85%B5%E5%99%A8#%E3%83%9C%E3%83%AA%E3%83%8E%E3%83%BC%E3%82%AF%E3%83%BB%E3%82%B5%E3%83%9E%E3%83%BC%E3%83%B3

This Wikipedia page in Japanese credits Nobuyoshi Habara for roughs and "林裕樹" for finishes. I'm not sure how to translate that, but the name also comes up as sub-mecha designers for Galvion and Srungle.

Habara also worked on Srungle, as well as Dorvack, Dancougar and Machine Robo among others. But the person who did the finishes, I can't find them anywhere.

If anybody knows that name, and knows more about the animator, let me know!

BINGO. The finishes are by Hiroki Hayashi. https://en.wikipedia.org/wiki/Hiroki_Hayashi

So assuming Japanese Wikipedia is correct, we have an answer.